Here is one sample that seems to cause problem. Really rarely it is playable, most of the time screen is blanc.
H264_profile.m4v

Video
Encoder: H.264
Res: 640*480
Frame: 29.97fps
Bit rate: 1500 kbps

Same file but with Xvid encoder. This is OK.
Xvid_profile.m4v

Before DSP updates and libgstdsp.so my 2nd N900 could play both files OK. After update both my N900 have difficulties to play H.264 file.