Hi hoops44,
I installed 3D Flash Gallery on Win XP SP3 and I don't get the error message that you reported. However, access violation errors can be caused by bugs in the software or corrupt files on your system.
Have you tried adding music in different formats (mp3, WMA, WAV) to see if the error is only generated by one format and not the others? When testing this issue, I noticed that even though the help file says that this software will play mp3, WMA, and WAV formats it does not recognize WAV files (only mp3 and WMA).
In the comment section, the developer of this software (Aneesoft) offered to answer questions via email (support@aneesoft.com). You could try reporting this problem to them, as it may involve a bug with their software.