Reporting Services Login Error

An error has occurred during report processing. (rsProcessingAborted) Get Online Help Logon failed. (rsLogonFailed) Get Online Help The parameter is incorrect.

I can view my report inside of visual studio 2003 no problem, but when I navigate to the http://servername/Reports/Pages/Folder.aspx and click on my report to load inside of IE I get the error. I have serached all over but not able to get a correct answer.
Any help woould be greatly appreciated.
Thanks

check your datasource to make sure it deployed properly and that the report is using the proper datasource (in properties)|||Yes.. its using the Source and be able to see the corrcet datasource in SQL manager. I am thining its more Login Setup, but there is not enough documents.|||It is definitely a data souce error, although it is a strange message. What type of credentials are used to connect to the data source?