SSRS rsReportParameterValueNotSet error

An answer to SQL Server Reporting Services (SSRS) rsReportParameterValueNotSet – “This report requires a default or user-defined value for the report parameter. To run or subscribe to this report, you must provide a parameter value” error.

We’ve just found a very strange reason for this error to occur. At the moment we can’s explain why this solution resolves the problem, but we will be looking into it. If you’ve got any insights, then please comment with your thoughts as to why this problem could occur.

The server being used is a Windows Server 2008 with SQL Server 2008. We’re generating a report through code using the standard ReportingService2005 and ReportExecutionService objects, calling GetReportParameters and SetExecutionParameters before finally calling the ReportExecutionService Render function to generate a PDF of the chosen report.

The report that we were having a problem with had just one parameter – SupplierID – a string value (actually a database GUID / uniqueidentifier) but converted to a string for the report.

Anyway: we were getting the rsReportParameterValueNotSet – “This report requires a default or user-defined value for the report parameter. To run or subscribe to this report, you must provide a parameter value” error.

The answer was to convert the GUID uniqueidentifier value to UPPER CASE before assigning it to the ParameterValue array!???

Thoughts on why this might be necessary are welcomed!