How to Fix TeamViewer Unable to Connect Unknown Session?

About the error "Teamviewer unable to connect unknown session"

If you see the “Unable to connect: Unknown session” error in TeamViewer, it usually means there is a communication issue between your device and the remote computer. Many users experience this when trying to start or resume a remote session. This problem may occur for several reasons, and understanding them can help you solve it more efficiently.

Network Connection Problems: Weak or unstable internet may break the link between devices, causing the “Unknown session” error or connection blocked after timeout. Try restarting your router or using a more stable connection.

Outdated or Mismatched Versions: When TeamViewer versions differ on both devices, the system may fail to connect. Updating the software on both sides usually solves this.

Incorrect Permissions: If the app lacks necessary permissions or is blocked by a firewall, it may not start a new session. Check your settings to ensure access is allowed.

License or Account Issues: An expired or limited license can lead to blocked or timed-out connections. Verify your account and license status to avoid disruptions.

By identifying these causes, you can fix the “Unknown session” problem quickly and restore normal remote access. Next, let’s explore some practical methods to resolve this error step by step.

How to fix Teamviewer connection failed unknown reason

Fix 1. Timeout setting for inactive sessions

To prevent your TeamViewer connections from being blocked because of inactivity, you can set a time limit for idle sessions. Here’s how to end inactive TeamViewer sessions:

Step 1. Open the Gear icon in the upper-right corner of the TeamViewer (Classic) app. Then, navigate to Advanced > Advanced settings for connections to other computers > Timing out inactive sessions.

Step 2. Choose a time period after which an outgoing remote control session will be automatically terminated if there’s no interaction within the set duration.

Fix 2. Restart TeamViewer and try again

Restarting TeamViewer can fix the “Unable to connect: Unknown session” error because it refreshes the connection between your computer and the remote device. This clears temporary glitches, resets network settings, and allows TeamViewer to start a new, stable session.

Step 1. Press Win + R, type in “services.msc”, then click OK.

Step 2. Find TeamViewer. Right-click it and then choose Restart.

Step 3. Wait for the process to finish. Then try to connect via TeamViewer again.

Fix 3. Reset the TeamViewer ID

When you reset the TeamViewer ID, the software assigns your device a new identity. Sometimes the old ID becomes damaged, duplicated, or restricted, which stops the connection from being recognized. A fresh ID removes these conflicts and helps the remote session connect normally again.

Step 1. Follow the steps above to stop TeamViewer from the Services first.

Step 2. Open Registry Editor by entering “regedit.exe” in the Run box. Navigate to: HKEY_CURRENT_USER > Software > TeamViewer. Delete the TeamViewer registry key.

Step 3. Open the PowerShell console with administrator privileges and run the following command to determine the creation date of the "C:Program Files" folder:

Get-Item "C:\Program Files" | select Name,CreationTime

Step 4.Use the NirCMD tool to change the creation date of the Program Files folder. Download it and run it from the elevated Command Prompt console as follows:

nircmdc.exe setfilefoldertime "C:\Program Files" now now

Step 5. Check if the CreationTime value of the directory has changed.

Step 6. Then, using one of the special tools available, change the MAC address of your network card. Alternatively, you can edit your MAC address through the registry by following the steps outlined below.

Step 7. To get the current MAC address of your network card, open command prompt, and run the following command:

Ipconfig /all

Pay attention to two parameters: Description (LAN card description) and Physical Address (MAC address).

Step 8. Then, open the Registry Editor again and go to the key: HKLM > SYSTEM > CurrentControlSet > Control > Class > {4d36e972-e325-11ce-bfc1-08002be10318}.

Step 9. Find DriverDesc option, where the description (name) of your NIC must be specified (for example, Intel(R) 82574L Gigabit Network Connection). When you've found the correct network card, double-click the NetworkAddress parameter. It specifies the network card's MAC (hardware) address. It is sufficient to change a single digit in the current MAC address, such as 000C299D4D80.

Step 10. As a result, the network card's MAC address is changed. You must now modify the VolumeID of the system partition. VolumeID (or Volume Serial Number) is a hard drive volume's unique identifier that is set during formatting. Use the console utility VolumeID v2.1 to change the VolumeID v2.1. VolumeId.zip should be downloaded and extracted.

Step 11. Open Command Prompt with Administrator privileges and run the following command to determine the current VolumeID:

vol

Volume Serial Number is 5E37-ECE1.

Step 12. Replace the current value with the new value 5E37-EC11:

c:\users\root\Downloads\VolumeID

Volumeid.exe c: 5E37-EC11

Step 13. Close the command prompt and restart your computer. Then restart TeamViewer, and you'll be given a new TeamViewer ID.

Fix 4. Use the best alternative to TeamViewer for free

If you have tried several methods but still cannot connect with TeamViewer, switching to a more reliable program can save both time and frustration. AnyViewer is a great alternative that provides secure, stable, and fast remote access while avoiding many of the connection errors that appear in TeamViewer.

AnyViewer lets you control multiple computers from anywhere for both personal and business needs. It supports attended and unattended access, allows file transfers, screen sharing, and permission management, and works with an easy, user-friendly interface. Another advantage is its flexible and affordable pricing. The cost can be much lower than TeamViewer, offering excellent value without reducing important features.

With smooth performance, strong privacy protection, and quick setup, AnyViewer is an ideal choice when TeamViewer cannot connect properly. In this part, we will learn how to use AnyViewer to create a stable remote connection.

Step 1. Install and run AnyViewer on both of your computers. Navigate to Log in and then Sign up on the Controller computer (if you have already registered on the official website, you can log in directly).

Step 2. You should now see that you have successfully logged into AnyViewer. Your device will be assigned to the account to which you have logged in automatically.

Step 3. Log in to the same AnyViewer account on the two devices, then you can click One-click control to achieve a direct connection, click View the screen to see another’s screen, or click File transfer to share files between computers.

Conclusion

In conclusion, the “Unable to connect: Unknown session” error in TeamViewer often happens because of connection issues, outdated software, or account settings. By checking your network, updating the app, and resetting your TeamViewer ID, you can usually fix the problem easily. However, if the issue continues, using a reliable alternative like AnyViewer can help you build a more stable and secure remote connection. It ensures smooth access and better performance without frequent interruptions.