So I was working with my customer and suddenly in one of the environment with SharePoint 2010 we saw some weird webpart error on one of our Pages and further debugging revealed that only one Web Front End was having the issue and other Front ends were working fine.
The error we looked thru ULS and found that :
executing web part: System.Exception: ResolveToken returned unexpected object type.
Microsoft.Xslt.MethodCollection.MethodDescription.SetCode(DynamicILInfo ilInfo, Int32 fixup, Byte ilCode, Byte ehTable, Int32 maxStackSize,
Microsoft.Xslt.MethodCollection.MethodDescription.DefineDynamicMethod(DynamicMethod dm, MethodCollection methodColl)
Tried to look around stuff and found nothing in the ULS log or even on the SQL Server permissioning, so finally out of curiosity just recycled the App-Pool for that web-application having the issue and that's it , it resolved the issue all WFEs now in good shape.