'Cast object of type' error - resolved by IIS recycle

Question

3rd party ASP.Net web site and web service installed. The code appears not to log errors to server log or custom error log.

User receives the following critical untrapped error message:

"System.Web.Services.Protocols.SoapException: Unable to cast object of type 'System.Security.Principal.WindowsIdentity' to type 'Library.Security.Identity'. at ....."

Of course I understand the type cast issue but why would a IIS recycle resolve the issue?

Answer 1

Software provider, provided solution - no explanation given but assumption held by @Aristos and myself still stand.