Does your PROC REPORT have LINE statements? There is an issue with PROC REPORT and Web Report Studio that you will just see a blank screen if your PROC REPORT has LINE statements? That's because the SAS Report XML does not currently handle LINE statements gracefully.
If you run the Stored Process in EG, for example, are there any error or warning messages in the SAS Log? Does the SP work in EG or in the SAS Add-in for Office? It is easier to get the log by running in EG? Do you get any Java error messages at all?
Did you move your SP to the BIP tree location? Sounds like you must have, but I'm just covering all the bases. Unless it's the LINE statement issue, the only other thing I can think of is that you called your parameters something that conflicted with JAVA/JavaScript -- macro variables named "VAR" or "CLASS" or any of the reserved Java names will also cause problems with WRS, as described here:
http://support.sas.com/techsup/unotes/SN/018/018502.html
Or this one...
http://support.sas.com/techsup/unotes/SN/019/019980.html
If it isn't any of these things, your best bet for debugging is to contact Tech Support.
cynthia