The OVER SQL Construct or statment is not supported.
Ok so reporting services can not deal with the ROW_NUMBER function no big deal I will just place the query in a SP and call that.
You can receive a similar error when writing a query in SSAS. I haven't checked Reporting Services, but it's probably the same dialog box. The query designer cannot handle the OVER clause, so in the dialog box where you can paste your SQL, try turning off everything except the SQL pane.