When you are experiencing the following issue in your SharePoint 2010 environment (in my case the error was happening when certain feature receivers had to be executed):
To enable assembly bind failure logging, set the registry value [HKLM\Software\Microsoft\Fusion!EnableLog] (DWORD) to 1.Note: There is some performance penalty associated with assembly bind failure logging.
do not start going to the registry and change the registry value. This error occurs usually when your SharePoint environment has been shutdown unexpectedly. Just restart IIS and everything should be working fine again. If that doesn't do the trick, then you can start to investigate.