Problem with erasing files

I am transferring my music library to my MyBookLive. Every once in a while the transfers stops, leaving me with one file on my PC and one on my MyBook. When I try to remove the file from the MyBook it takes forever. Removing an empty folder on the other hand is no problem. It sometimes claims the file is in use, which it isn’t.

Why is this?

The same happens to my MBL 3TB. I tried to erase the files in the MBL and was incredible slow. It erased at the rate of 5-8 items/second. However I got >1000 items/second in my desktop.

Please, someone help me!!!