Q: error 36 when trying to copy itunes folder

I am not very computer savvy and have searched for some sort of solution to this issue.  I have an ext. HD western digital and since mavericks I have had issues accessing this drive.  It is very slow.  So slow that it really doesn't work at all and I can't seem to copy files off of it anymore.  Before mavericks I put my itunes folder on this drive to save some valuable space on my imac and now can't access my music or movies in itunes.  I have tried to relocate this folder to another ext HD but I keep getting the following error. "the finder cannot complete the operation because some data in "download.m4a" cannot be read or written (error code-36)". What if any is the easiest way to make itunes a useable app again with my music and movies?  Many thanks for any help.

Tim