System.IO Woes

I've been working on a Web Deployer windows application the last week or so, and everything was working great until I refactored some code the other night.  In a separate thread, I'm traversing through a directory (and subdirectories) getting the size of all the files needing to be copied.  Just after that, I start traversing through that same directory, attempting to copy the file to a destination. However, after refactoring code into 1 method for all the traversing, I've been unable to copy any of the files, and am getting a "The process cannot access the file ... because it is being used by another process."

If you have any idea or could help me out, that would be great.