Sorry I forgot this is a multi value parameter, they don't hold data the same as a single value parameter, so these comparisons will fail.

I can't really test this, but I think you need something like this:

=IIF(InStr(JOIN(Parameters!clmType.Value,","),"P") > 0,IIF(InStr(JOIN(Parameters!clmType.Value,","),"I") > 0,"List of Professional & Institutional Paper Claims ", "List of Professional Paper Claims "),"List of Institutional Paper Claims ")

Doulbe check I got the ( and the ) in the right places and the right quantity, it is hard to do this without the expression editor.