Issue while using embedded vb code in SSRS 2005

    I am using the function to embedd within the report .This function is called the user presses the view report button.

It works in the report designer (in preview),but it doesn't work on the server after i deployed it to the server,
why does it give me the message that is Error during processing of '@ParameterName' report parameter.(rsReportParameterProcessingError).

I am using Mgbox to display some alert statements in the Custome code.. embedded into the.. report

do I need to do anything with custom assemblies?
or any ot
her reasons this?

Any help to solve this issue is greatly appreciated

Regards,
Kay