Does the forum logs give an error when it crashes?
Do you have mongo and nginx logs on?
There should be some useful information in one of the logs as to what is happening.
Whenever I try to spin 0.4.x up, the following error occurs in the log:
[cluster] Spinning up another process... [cluster] Child Process (*) has exited (code: 8)
What could be the problem?
Clustering wasn't available in 0.4.x I don't think. So either you've got newer files on your server than 0.4.x, or 0.4.x has become self aware and is mimicking the newer models.
Too spooky, hasn't Terminator taught us anything?!
I reinstalled in a new directory and that fixed it.