My dad had exactly this error when he was trying to move some stuff off of his old machine onto an external drive. He had some names like "Process and Integration April 2008", with similarly named folders going a few levels deep and files with equally long names at the bottom; didn't take long for the path length to hit the (I think) 255-character limit.
We just renamed the directories to make the names, and ultimately the paths, shorter - starting at the top level and working down - then tried the copy again. Took a couple of goes before we nailed everything that was over the limit, but it worked and we didn't need any special software.
rsync
.