Help!

After Making some hundreds of well-Working Polyphonic Ringtones for Nokias, there's Still One Big Question:

Why do some SP-Midi-Files not work???

- We've been Testing them on a nokia 6610, and they never were bigger than 8KB. The MIP was set to 4, with therefore no values bigger than 4, and only controllers necessary (Vol, ResetCtr, PC).

Whats bizarre is, is that other files wich look perfectly the same, work fine while some just dont. Sometimes after decreasing the number of tracks, they started to work, so one guess is, it could have something to do with size/complexity?!?!?

So anyone with answers please let us know. Thanx.