CCRL games in Chessbase's reference search : not enough grand master games I downloaded a PGN of CCRL 40/15 games from

http://www.computerchess.org.uk/ccrl/4040/CCRL-4040-commented.[1138203].pgn.7z

and opened it in ChessBase, and converted it into a cbh. (I can even put this database as reference database but it doesn't change what follows.)

Then in the reference search I chose this database as "reference database", and try for instance to search for games starting with the 1.e4 move by imputing this move on the board. There are plenty of them.

But the reference search tells me "not enough grandmaster games".

Where are the reference search options that I have to tweak to make this obvious thing work? Should I change the games perhaps, so that they could be recognized as grandmasters games?
Maybe the best games filter in reference search window enabled (checkbox).