There is a similar thread that answers the same kind of question. Please check if it helps.
http://social.msdn.microsoft.com/forums/en-US/sqlreportingservices/thread/bb49d7be-e9fa-4439-b46c-5ead51a6feeb/
Also refer to this KB article
http://support.microsoft.com/kb/909678
Please mark the replies as Answered if they help and Vote if you found them helpful.