One other possibility is that the format you are using for entering the dates is different than the format you have asked PAF to expect in Tools menu > Preferences > Formats
If they agree, PAF shouldn't object. Also experiment to see whether or not PAF expects the comma in the format you are using.
I use the International ("European") format e.g. 1 May 2007 ... which is the format I asked for in Preferences. I never have any date error messages except when I try to input the Place in the Date space.