The wrong thing has gone wrong;-)
This forum has recently been flooded with the help-me/how-to "something has gone wrong" which I wish would be removed or sunk rather than fill the page. This entry is different for I suggest that I have encountered the issue myself and while I was able to solve it by searching this forum, I think that it would have been better not to have the issue in the first place.
A quick scan of this forum gives me the sense that the issue often encounters people who try Vanilla for the first time. Thus, I'd think that it is in Vanilla's best interest to avert this relatively common issue in the first place.
My suggestion to the Vanilla lords:
1. Include tests within the install process to verify that the proper access rights are set (and clearly inform the user what needs to be done if they are not).
2. Further emphasize the required access rights setting in the installation instructions.
I concur with one of @hgtonight 's feedbacks to one of these discussions that if so many users encounter this issue then it should be addressed at the root (no pun intended ;-)