There're 3 reasons that causes this error:
1. Invalid Path to Temp-folder
2. tmp folder not writable
3. Your Download-ID is invalid
@adminbe
You've reached the download limit that's why the Download-ID has become invalid. I've increased your download limit and re-send you the new Download-ID.
@toomanylogins
I can't find any order of you (VirtueMart sucks) so plz, paste here your order ID:
www.joomace.net/e-shop/account
The current download system counts every automatic upgrade as a download so for now use the manual upgrade for multiple sites. This issue will be solved soon.