Weird. Editor crashes on 2nd Play, doesn't happen in build

Here’s a problem I have been struggling with for months now. I ran it by some Unity support techs but their only suggestion was to upgrade to Unity 4. (which I did to no avail).

Whenever I try to run my game inside the unity editor the 2nd time after loading up Unity, the editor crashes. The game works just fine the first time it is played when Unity is launched, and this problem doesn’t happen in either a Mac standalone build or iOS build. It only happens on the 2nd play attempt. This only happens in one scene (the main menu).

I am using NGUI and several Prime31 plugins, but I have updated everything to the latest versions (including unity). What could possibly be happening that a crash occurs only on a second play? Something getting left inside memory?

The console doesn’t help either:

Receiving unhandled NULL exception
Launching bug reporter

*** Launching bug reporter due to crashbug.
Obtained 0 stack frames.
Ignoring invocation of an instance method on a NULL instance.

Did a google search for: unity Obtained 0 stack frames.

Prime31 seems to be known to cause that error

http://webcache.googleusercontent.com/search?q=cache:smile:49qCdcCNe0J:prime31.com/support/261/prime31kit-crashes-unity-on-every-launch-log-included+&cd=4&hl=no&ct=clnk&client=firefox-a

http://webcache.googleusercontent.com/search?q=cache:cjZNNheNYPcJ:prime31.com/support/222/p31restkit-error-crashing-unity-project-load-attached-help+&cd=2&hl=no&ct=clnk&client=firefox-a