File Name Conflict when backing up to external HD

As I was backing up a folder containing several files to an Iomega Ego 2 TB external hard Drive, I received an error for a file stating that there already was a file with the same name in the folder. However, the file names, sizes, etc of the two files in conflict were completely different. There is nothing to relate these two files to one another, and I could not understand why the computer thought there was a file name conflict between these two files. Renaming one file or another would fix the conflict, but there should have been no conflict to begin with. I could copy both files to other external devices without a problem. Eventually, the iomega external HD allowed the two files to be copied into the same directory and every subsequent attempt to copy these two files into the same directory has not resulted in any conflict. Why would there be a same file name error with two files that do not have the same name?