My program is unable to File.Move or File.Delete a file because it is being used "by another process", but it's actually my own program that is using it.

I use Directory.GetFiles to initially get the file paths, and from there, I process the files by simply looking at their names and processing information that way. Consequently all I'm doing is working with the strings themselves, right? Afterwards, I try to move the files to a "Handled" directory. Nearly all of them will usually move, but from time to time, they simply won't because they're being used by my program.

Why is it that most of them move but one or two stick around? Is there anything I can do to try freeing up the file? There's no streams to close.