I had the same problem, annoying isn't it.
What you need to do is to eliminate the source file causing this.
I found an unusaul file on my hard drive. It was titled TEMP, it too was a zip file with the exact same size of 400kb.
Do a general serach on your computer for it and eliminate it, it should also be accompanied by an x + y text file, delete these too.
At the same time delete ALL the files in your shared folder, i mean EVERYTHING!!! It only worked and dissapeared for me when i deleted all these files.

Then empty out your recycle bin.

This worked for me, not too sure if its the same for everyone else!