Vagrant Not Starting Up. User that created VM doesn't match current user

I ran into the same problem today.
I edited my UID by opening the file .vagrant/machines/default/virtualbox/creator_uid and changing the 501 to a 0.

After I saved the file, the command vagrant up worked like a champ.

NB: the .vagrant folder is in the same directory as your Vagrantfile, where you ran vagrant up

Ran into this problem in a slightly different situation. The issue was that ".vagrant" was checked into the git repo, and the committer was running under a different UID than I was.

Solution: add .vagrant to .gitignore.

I ran into the same issue, but in my case it was because I had ran vagrant up under sudo, and when I came back to it later I'd forgotten.

Silly mistake, but I'm sure it's not the first time it's happened someone :)