Usually, this is a problem with the format of the date and time of observation. See bellow for more information.
Unfortunately, there is not any standard how to save a date and time of observation to FITS file, so every program uses its own special format. Although current version of C-Munipack can read many different formats, it may happens, that your program uses the another one. Send me one frame or two as sample (see Bug reports, new feature requests) and I will add it to the sources promptly.