This video shows how to fix the Error ACS50008 in the context of Microsoft Azure Access Control Service. This error usually is displayed as an Inner Message like this:

An error occurred while processing your request.
HTTP Error Code: 401
Message: ACS20001: An error occurred while processing a WS-Federation sign-in response.
Inner Message: ACS5008:SAML token is invalid.
Trace ID: 903f515f-3196-40c9-a334-71277700aca6
Timestamp: 2014-03-02 10:16:16Z 

Links:

How to fix Error ACS50008 https://msdn.microsoft.com/en-us/library/windowsazure/jj571618.aspx

ACS Error Codes https://msdn.microsoft.com/en-us/library/windowsazure/gg185949.aspx

ACS Documentation https://msdn.microsoft.com/acs