This exception occurs when DotImage attempts to verify the license file. DotImage requires read and write access to the Machine Key directory, usually located in in the folder
"C:\Documents and Settings\All Users\Application Data\Microsoft\Crypto\RSA\MachineKeys".
Be sure to grant read/write permissions to the appropriate users (ASPNET userfor ASP.NET applications). By default this folder will have the required permissions unless it has changed from the initial OS install, however there appears to be a bug in windows that mistakingly sets this folder to read only when adjusting file permissions.