In case the below actually ends up helping, I'm posting this here for others to try if they encounter a similar error.
There is a known issue with Java on Windows XP where Java misreads the System's timezone. More details below, but in short, there is a bug in the Java implementation from Sun. The Java API is not able to translate all possible Windows XP registry timezone patterns to equivalent timezone representations, which leads to problems. It's a weird issue that happens on a select percentage of machines out there.
The supposed fix, as lame as it seems, is to do the following:
1) Change your System timezone to something else. Any random change will do. Apply the changes.
2) Change your System timezone back to the correct timezone. Apply the changes.
This should set the timezone in the Windows registry so that Java will correctly read it. After doing that, the next time you run d20Pro, everything should work.
For details on this, see the following article:
http://techtavern.wordpress.com/2010/04 ... indows-xp/This may or may not be a fix for this problem, but it seems a likely solution.
--Glav