Hosting is shared or dedicated? Version 2.4 is pretty hefty in what is required to run it, so I assume that with the exception of restoring courses from 1.9 versions, there are no other issues with the install.
In assiting others with problem 1.9 course restores, in each instance, max_allowed_packets had to be increased for MySQL - plus other MySQL tweaks depending. Moodle 1.9 courses don't have to be large as far as the size of the backup zip, it's more the contents of the course and what Moodle 2 has to do to convert the course to a .mbz before it attempts to restore.
Check your moodledata folder temp/backup/ for clues that might led to resolution of the problem. That you should be able to do. Might also suggest that to service providers help desk.
'spirit of sharing', Ken