Problems with STS

[Strayph]

Hello,

I started writing some Grails unit tests, and then started getting 'class not found' errors.
These literally just started popping up, even though the test has just passed a few minutes ago.
Then it got worse, and the Spring Security plugin classes started not being found.

I probably should have immediately come here and asked about it, but instead thought I would update STS.
I updated STS, and it was apparently 2.7.1. (If I remember correctly...)

Because now it won't start at all. It just hangs on my Mac.
I have killed it and restarted, to no avail.

Is there a way to reset STS somehow?
And where did all these "ClassNotFound" errors come from?

Thanks,
Strayph