Nokia C2-03 supports the following video formats 3GPP (H.263), H.264/AVC, MPEG-4 and WMV. Even though your device is able to play 3gp videos, there are certain limitations due to the technical specifications of your phone. Please see here for more details.
Your device can play only 15 frames of video per second, which on it's own could cause this problem. Also, the video in question may have higher resolution than supported.
What you can do is to reduce/convert the video file resolution into what your phone supports and see if it allows you to play the file.
Hope this helps,
Try the Soft Reset code *#7370# followed by 12345 (default security code unless set by you ) when prompted. This code did not work on the earlier S40 devices but seems to work on the recent ones ..and back up important data before doing ..