Connection Could not Be Established. Reason Unknown.

I Tried to Connect to Partner system by using the Same version, I'm getting the error message that A Connection Could not be Established. Reason Unknow. But my Partner is Able to Connect to my System. I tried to Connect to other partner Systems and successfully connecting to those systems too . Anybody help about to solve the issue?



  • mLipok
    mLipok Posts: 781 ⭐Star⭐

    Did your partner try to close and start again TV on his computer ?

    mLipok , AutoIt MVP
  • Abelardor
    Abelardor Posts: 1

    The partner that I am trying to connect has restarted his computer and still I can't connect.

  • How did this error get fixed im having same issue.

  • saeme issue here to...would love to find out how to resolve.  people can't conenct to me.

  • I rebooted the host computer (Windows 10 / Teamviewer 12) and now neither of my two clients can connect to it.  Before the reboot, only one client was having problems.

    Any suggestions?

  • mLipok
    mLipok Posts: 781 ⭐Star⭐

    Recently I have similar issue .
    After TV host upgrade on RemoteHost (from TV9 to current) there was problem with Instalation as on RemoteHost there was only 17 MBytes of free space on System Drive !!!

    After system Clean Up I get 18 GBytes so the TV upgrade was properly ended.
    And now I can normally login.


    mLipok , AutoIt MVP
  • At least for me the problem is gone now.

    I don't know if it relates but I forced a password change with my teamviewer account, then rebooted the host PC and the client PCs.  They failed to connect to the teamviewer server at first, but after I changed the password on each, everything started working.

    I've tested my one "server" from for different clients.  All are working. 

  • RDrays
    RDrays Posts: 1

    Had the same problem after having installed the latest iTunes.
    Try disabling/stopping the "Apple Mobile Device Service" service before starting Teamviewer.
    That fixed my problem. Good luck

  • I have this issue for two systems. I am able to get into those systems using other softwares, but TeamViewer pops up this message when I try to connect. The above mentioned solutions didnt work for me.

  • ammar91
    ammar91 Posts: 1


    @GregFreemyer wrote:

    At least for me the problem is gone now.

    I don't know if it relates but I forced a password change with my teamviewer account, then rebooted the host PC and the client PCs.  They failed to connect to the teamviewer server at first, but after I changed the password on each, everything started working.

    I've tested my one "server" from for different clients.  All are working. 

    I am also facing this issue but no solution is working for me.

  • Many connections not working (same issue here) and there is no update? No response from TeamViewer?

    Instead of a fix, could someone suggest me another app/program?

  • Another TV alternative for Windows is AeroAdmin. You can download it from here -

    [competitor link removed by Moderator]

    FYI., this TeamViewer error 'Connection Could not Be Established' got resolved by itself. The only thing I remember I did was updating it to the newer version.



    Syed Abdul Raafay

  • walldoo99
    walldoo99 Posts: 5 ✭✭

    I found that logging on to my VPN lets me connect, but any other attems directly fail to all computers. This has been going on for a long time. Windows 10 Pro, AT&T fiber optics


  • DesertSweeper
    DesertSweeper Posts: 23 ✭✭

    Which versions of Teamviewer are being used - you should NOT use version 13 yet - on either side. It has issues. Wait for them to release a more stable version. For now I use version 12 on both sides and all my issues went away

  • Fixing blacklist and whitelist fixed it for me

  • I'm getting the a pop window that says "unable to connect" teamviewer not running on partner computer.  it is running.  The computer that wont' connect is my home computer.  I have my wife wake up the computer by touching any key on the keyboard and then it shows online.  

    This was working find for months. I assume either a teamviewer or microsoft update caused the problem.  I uninstalled teamviewer on my laptop and home computer and reinstalled and they did not help.  Any ideas, i.e. something changed in version 13?

  • Which OS are you using? My windows 10 based teamviewer is working fine even after update.

    Although, I have one running on my linux machine. It stopped working presumably after updating to teamviewer 13. But I was able to get it back to work after fiddling with its 'Blacklist' and 'Whitelist' settings in its options (Extras -> Options -> Security for windows). 

  • I'm using Windows 10.  What did you add to the white/blacklist i.e. or something else?

  • You should verify the settings in the affected computer (one that's inaccessible)

    They can be accessed by the teamviewer application (Extras (in title bar) -> Options -> Security -> Blacklist and Whitelist

    I will recommend adding the other computer to the whitelist of the affected one, so it should be always accessible

  • DesertSweeper
    DesertSweeper Posts: 23 ✭✭

    This has nothing to do with white or blacklists. The computer is already accessible to you. It is just going to sleep.

    It sounds to me like your computer is going to sleep, entering a semi-shut mode where teamviewer and other running services are suspended. Your wife wakes up the computer and teamviewer along with it. Search for "sleep" and look through the settings of the "Change when the computer sleeps". Try setting it to stay awake permanently, and if that cures it - go in again and start to adjust power settings until you find the culprit. There are settings under "advanced" that can affect running services.

    As an aside I rolled back to v12 as there are very specific issues with 13. I always advise waiting for at least 6 months after a major release before upgrading.

  • FYI, I changed the timeout/sleep settings and I can connect unattended now although now my screen at the home computer no longer goes to sleep to save on electricity.  It worked before so I assume updating to version 13 caused the problem.  

  • DesertSweeper
    DesertSweeper Posts: 23 ✭✭

    Yes, it is a power thing. I doubt that v13 caused the problem, though as stated before, there are other issues with it - which is why I reccomend and use v12 despite having purchased the v13 license. Now as for you power issue, it is likely that the settings were inadvertantly changed, or an MS patch has modified your power-settings. I do not use Windows 10 (still and always will be on 7) but I am sure there are similar settings. As I said above, look for "Advanced Power Settings" or something similar. There you will find many options to fine-tune your power-management. It will probably be there that you find your solution to having the computer remain awake but still save power. Things like turning the display off and some hardware features, but still having esssential services run like TV. Try them one-by-one and you will find the culprit.

  • Sam27
    Sam27 Posts: 1

    Hi all, I had this problem just now, I logged out teamviewer and logged in. All fine then. Hope it helps. Cheers!

  • DesertSweeper
    DesertSweeper Posts: 23 ✭✭

    When people like "Portmeyers" above post their problems and you give them a solution, and they don't bother acknowledging it with a simple thanks, it makes one less and less inclined to help the community. It is not as if we are employees of TV and we are under no obligation to respond to help requests. Why bother

  • walldoo99
    walldoo99 Posts: 5 ✭✭

    a lot of people are going back to 12 and it works fine. I find using my VPN makes it work fine

  • Roughly 50% of my Partner list has Blue Question Marks suddenly and Connection Could not Be Established on 50% of the ones that look ok in my list.

    Was ok first thing this morning.

  • Warhangel
    Warhangel Posts: 1

    TW are changing the IDs so i think we have to wait a bit more time

  • sargavely
    sargavely Posts: 1

    Was your issue resolved?  I am having the same problem..

  • hajo1003
    hajo1003 Posts: 2

    @twodays ago everything was ok but as I connected to TV most of my clients has blue question mark and I could not access them. All the other ones no problem. IWe are running TV 5.1.17330 since 8 years with out any problems. Did you got your problem solved?

  • hajo1003
    hajo1003 Posts: 2

    The reason I cannot connect to a certan client is that TV changed the ID of clients on 07-24-18 without notification. Customer support recoments to close/ restart TV for each client. I did this and it worked out for me. I hope for you too.