OK, I will reapply my MM4 registration code, and see if it happens again.

it must be in what you did as I am not seeing any problems with my registration.

It have a registered Gold copy of MM4
I tested the latest version of MM5.
Now my version MM4 thinks that that it (MM4) is an unregistered copy.
* I see the MM4 "MediaMonkey Gold" menu for unregistered versions
* the About screen says I am running a standard unregistered version
* I no longer can edit collections in MM4

Things that may help:
* when I was in MM5 I tried to edit a collection via Tools|options|library|mediaTree ... it said that i must purchase Gold
* I then tried editing the collection via right click a node on the Media Tree ... it allowed me to edit the collection OK .. ?
* later I was testing some of the MM5 GPM integration ... and while there i started MM4 while MM5 was running ... this didn't use to create a problem

Something has wiped out my MM4 registration details
I rebooted ... the problem persists.
I installed the latest MM4 beta (ie. 4.1.21.1868) ... the problem persists.