Cannot open Word 2003 file in Word 2007

I have a user who sends me Word 2003 files that I cannot open on one PC using Word 2007. What really is confusing are two factors: 1)I can open the files on another PC using Word 2007; and 2) on the problematic PC I can open other Word 2003 files, but cannot the ones from this particular sender. The files have been sent on separate occasions.

I have done an Office repair on the PC to no avail. What could be causing this perplexing problem?

Thanks!