Install-SPUserSolution : Sandboxed code execution request failed.

This is a really tricky error I had when trying to deploy a Sand-boxed Solution using PowerShell on a new farm.  The error “Install-SPUserSolution : Sandboxed code execution request failed.”  happened with PowerShell, and with the GUI.

(opens in a new tab)

I looked in the ULS log and found this:

Sandboxed code execution request failed. – Inner Exception: System.InvalidOperationException    Server stack trace:      at Microsoft.SharePoint.Utilities.Verify.DoFailTag(UInt32 tag, ULSCat category, Type type, String format, Object[] args)     at Microsoft.SharePoint.Utilities.Verify.IsTrueTag(UInt32 tag, ULSCat category, Boolean expression, Type type, String format, Object[] args)     at Microsoft.SharePoint.UserCode.SPUserCodeExecutionHost.Execute(Type userCodeWrapperType, Guid siteCollectionId, SPUserToken userToken, String affinity, SPUserCodeExecutionContext executionContext)     at System.Runtime.Remoting.Messaging.StackBuilderSink._PrivateProcessMessage(IntPtr md, Object[] args, Object server, Int32 methodPtr, Boolean fExecuteInContext, Object[]& outArgs)     at System.Runti… 28b119be-321a-42d6-892a-b7ddcf358e74

With no results on Google on how to fix this issues I tried a lot of things without ever being able to replicate it on another machine.

What I found is that there was another related error  :  (You can also check fix for this specific error here (opens in a new tab))

Unable to load assembly group. The user assembly group provider threw an exception while trying to provide user assemblies for the specified assembly group.

The Fix:

I added the Service Account running the Sandbox Service with Full Control rights on the Web Application (User Policy) and it worked. 

I deleted the Web Application and re-ran the script (without re-adding the Full Control rights) and it worked no problem.  

Say thanks if this helped 🙂