When my girlfriend sends me a video on her cell phone some videos will say unsupported video file or unsupported file type how can i fix the videos that show error message?

well, what is the file format of the video?

depending on the file format, you'll need various codecs to play the video back...

also, if you are trying to watch the video ON a cell phone, odds are you will never be able to watch it on that cell phone- the codecs aren't easily updated on cell phones.