Thanks to everyone who replied (and especially to everyone who contribues to the great SCID project)! Ok, "I" did make this error. However, the PGN was scraped from a Website, so that is where the error came from (and I did not notice ...). Also, in chessbase reader it is recognized without a problem. But thanks for the hint - I will check the other castling notations scraped as to whether they use zeroes or O's and maybe it is just a glitch at that particular spot (the only spot where SCID complains)....
Unknown token "0-0-0+"