How to fix SharePoint 2010 excel service error "System.IO.FileLoadException: Loading this assembly would produce a different grant set from other instances"?

If you enable to display excel file in browser on SahrePoint 2010, you could setup using the following steps.

Go to list library such as Shared Document -> Library -> Library Settings->Advanced settings->Opening Documents in the Browser -> select "Open in the browser".

However, we run into error listed bellow:

ExcelService.PostProcessRequest: Excel Server Exception: System.TypeInitializationException: The type initializer for 'Microsoft.Office.Excel.Server.CalculationServer.ExcelServerApp' threw an exception. ---> System.IO.FileLoadException: Loading this assembly would produce a different grant set from other instances. (Exception from HRESULT: 0x80131401)     at Microsoft.Office.Server.Diagnostics.FirstChanceHandler.ExceptionFilter(Boolean fRethrowException, TryBlock tryBlock, FilterBlock filter, CatchBlock catchBlock, FinallyBlock finallyBlock)     at Microsoft.Office.Server.Diagnostics.ULS.SendWatsonOnExceptionTag(UInt32 tagID, ULSCatBase categoryID, String output, Boolean fRethrowException, TryBlock tryBlock, CatchBlock catchBlock, FinallyBlock finallyBlock) .....

In order to resolve this issue, you could try the following procedures.

1. Verify Excel Services Application is running correctly from central admin
2. Verify Excel Calculation Services is in Started status
3.  Restart the Excel Calculation Services

If Excel Calculation Services restart could resolve it, the worst case is you need to restart SharePoint 2010 servers and this issue should be resolve. I'm not sure the root cause of the issues right now. If you have better idea on this, please share with me.