I've had the same problem, un- an rechecking "Allow Server Reports" didn't solve it (as it's already been checked). This was the solution for some people: Any idea why the Select Report drop down is greyed out?
Related to the error message, i looked for printers installed on the server: no printers have been installed.
So the solution was rather easy: I installed PDF-Creator (watch out for search-bars, etc. which are included in the installation-routine, better choose "Custom installation") and it works fine.