Dynamics AX 2009 reporting service error

I used to get this error message when opening reporting service from Ax :
Error during processing of ‘AX_CompanyName’ report parameter.
(rsReportParameterProcessingError).
Even this error occured in the AX 2009 VPC that previously works perfectly.

This information from partnersource (requires partnersource login) says that in SQL Server 2005 the execution account should not be used, and in SQL Server 2008 it is set to BC proxy account.
I am using SQL Server 2005, so I clear the execution account in the SSRS configuration (Start > Program > SQL Server 2005 > Configuration tools > Reporting Services configuration. In the execution account part (the bottom one), clear the option 'specify an execution account'.

Hope this helps many people trying to solve the same error message.