I am having a similar error and was wondering if there was a solution for the issue. I have tried to auto update and then customize it so the defs were the only thing I was downloading but still no avail.
In the other user's case it turned out to be due to use of the case-sensitive file system (which is not supported). Are you also using it? If not, can you gather and send the information as outlined earlier in the thread?
You are running an old version of NAV (10.1.1) for which we no longer support virus definitions update via LiveUpdate. You can still get the latest definitions here: