How to fix "The WinRM Shell client cannot process the request. One of the parameters required for the WSManSignalShell function is null or zero."

Error Description

This error occurs when the Windows Remote Management (WinRM) client attempts to send a control signal (such as terminating a process or closing a session) to a remote shell, but the underlying WS-Management API receives an invalid, missing, or zeroed parameter (WSManSignalShell). This typically points to a configuration mismatch between the local client and the remote host, corrupted shell session states, outdated Windows PowerShell/WinRM components, or restrictive network security policies blocking the specific signal payload.

Step-by-Step Fixes

Step 1: Restart the WinRM Service

A glitched or frozen WinRM service on either the local computer or the remote server can cause parameter delivery failures. Restarting the service refreshes the state.

1. Press Windows Key + X and select Terminal (Admin) or Command Prompt (Admin).
2. Type the following command to stop the service and press Enter:

   net stop winrm

3. Type the following command to start the service again and press Enter:

   net start winrm

4. Perform these steps on both your local machine and the remote target machine if possible.

Step 2: Update or Re-register the WS-Management Components

If the local system files responsible for WSMan functions are unregistered or corrupted, WinRM may pass null parameters.

1. Open Command Prompt as Administrator.
2. Run the following command to reset the WinRM configuration to its default settings:

   winrm quickconfig

3. Type Y and press Enter if prompted to make changes or enable the firewall exceptions.

Step 3: Increase WinRM MaxShellsPerUser and MaxMemoryPerShellMB

When a remote shell runs out of allocated memory or exceeds the allowed number of concurrent shells, it drops or corrupts incoming session packets, leading to null values in function calls.

1. Open PowerShell as Administrator on the remote machine (or locally if troubleshooting local loopbacks).
2. Check the current limits by running:

   Get-Item WSMan:\localhost\Shell\*

3. Increase the maximum memory allocated per shell to ensure the signal payload is not dropped:

   Set-Item WSMan:\localhost\Shell\MaxMemoryPerShellMB 1024

4. Increase the maximum number of concurrent shells allowed per user:

   Set-Item WSMan:\localhost\Shell\MaxShellsPerUser 30

5. Restart the WinRM service using the commands from Step 1 to apply changes.

Step 4: Add Target Host to TrustedHosts List

If the client does not fully trust the remote endpoint, certain advanced management signals like WSManSignalShell may be stripped due to security restrictions.

1. Open PowerShell as Administrator on your local client machine.
2. Run the following command to trust the specific remote machine (replace REMOTE IP OR NAME with your actual remote computer's IP address or hostname):

   Set-Item WSMan:\localhost\Client\TrustedHosts -Value "REMOTE IP OR NAME" -Force

   (Note: Use `` instead of the name if you want to trust all hosts for testing purposes, though this is less secure).*

3. Restart the WinRM service on your local machine.

Step 5: Verify PowerShell and .NET Framework Compatibility

An incompatibility between the version of PowerShell running on the client machine and the version running on the remote host can cause serialized parameter objects to unpack incorrectly as null.

1. Check your PowerShell version on both machines by running:

   \$PSVersionTable.PSVersion

2. If one machine is running an outdated version of Windows Management Framework (WMF) or .NET Framework, download and install the latest updates via Windows Update to ensure both endpoints use matching protocols.