Just found out more information. The problem is that I had 2 prf files with a key of 2. So the problem is simply that the error message is wrong. It should tell you that there is a conflict in the keys of multiple prf files, not that the preference is not a single digit.
Just found out more information. The problem is that I had 2 prf files with a key of 2. So the problem is simply that the error message is wrong. It should tell you that there is a conflict in the keys of multiple prf files, not that the preference is not a single digit.