I agree with Colby, its definitely not the size of your databases that is causing the problem, my music DB is 6,884 KB ( 17000+ songs
) and XL loads it with no problem.
Your problem is most likely 'illegal characters'. Look for (') apostrophes, (#) pound and (&) single ampersands in your databases as they are illegal characters/values in XML field names and will cause the problems you are experiencing. The fact that you can load one or two movies just means that the error isn't in the first two entries
I.E.
This is bad a bad XML title -> Joe's_#4 concerto_for_banjo&flute
This would work -> Joes_number_4_concerto_for_banjo_and_flute
The easiest way to do this would be to open your music.xml database in notepad and just do a search one for each of the characters (', #, &) and if you find an entry with the offending characters - go to that mp3 file and edit the title to remove any illegal characters - then either re-import or edit the XML DB to match the new name.
For those of you looking for more detailed programming info on legal/illegal XML characters refer to this:
http://www.w3.org/TR/REC-xml
and look at at section 2.2.