Report Processing Error / Query Execution / incorrect syntax

My report has three parameters (year, class, area) and there is no issue with picking one parameter from each. When  I choose 'Select All' or when 2 or items are chosen in a single parameter dropdown list, I am get this error:

An error has occured during report processing (rs Processing Aborted)
Query execution failed for data set <dataset> (rs Error Execution Command)
Line 3: Incorrect syntax near ',',

In the main query the only ',' are in the SELECT statement. Of course, commas do appear when more then one item is selected in a parameter ( i.e Class parameter: Class 1, Class 2)

If anyone has encountered this, your guidence would be greatly appreciated!

Thanks,

NinjaDragonfly