SSRS Error : sys.webForms.PageRequestManagerServerErrorException 500

Hi all,

I've create ssrs report in VS2008 on my DEV env  and all works fine,

when I moved it to my customer env and run from the AX I'm getting this error : 

"Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server. The status code returned from the server was: 500"

any ideas??

thanks in advance,

Haim S