The value expression for the query parameter contains an error: the expression that references the parameter does not exist

I'm adding a new parameter, ReportView, to several reports. For some reports it works just fine, and with others I get the error:

The value expression for the query parameter @ReportView contains an error: The expression that references the parameter 'ReportView' does not exist in the Parameters collection.  Letters in the names of parameters must use the correct case.

I know the parameter name is spelled correctly.  In fact I've copied it from a working report to a non-working report.  I went so far as to copy the entire XML from a working report to a non-working report. Same error.  I cannot figure this out as to why it affects some reports but not others.  My steps are the same every time: add the parameter to the report, add the parameter to the stored proc, go to my dataset that is using the sproc and "refresh fields", then map the new report parameter to the sproc's parameter.  Then try to run the report.  Half the time it works and half the time it doesn't.  Can anyone tell me what I might be missing?

Thanks in advance.

André