At a course in the great state of Pennsylvania we just came across this intriguing problem:
On one installation, whenever we tried to import .episerverdata packages it would complain with an error message indicating that access was denied when writing to the Temp folder under the local user settings. After troubleshooting a bit and trying to allow whatever role we could think of, we finally ended up cleaning out the Temp folder entirely – and that did the trick. Perhaps we just hit that unlucky combination of two randomly generated temp names being identical – what are the odds? (First one to respond with an exact odds-calculation in the comments wins a beer at the next EPiServer event).
Anyway – solution: Clean out the Temp folder.