We had problems with crashes etc. on all versions of Powerlog until v4.0.37 which fixed a memory leak which seemed to cause it to lock up. It doesn't sound as if you have had that problem but it may be worth updating anyway.
However the OP said they were using Powerlog v3 - so they probably can't upgrade to v4 without paying for an upgrade.
The final version of Powerlog v3 is very stable in my experience, only issue I know is that exporting mono audio from a stereo log in Powerlog v3 client sums the left and right channels, without any level reduction resulting in clipped audio if your record level is high. This is resolved in Powerlog v4.
I'd double check that you have the correct log selected in the client and that you are not trying to access some remnants of the old system. I'm not sure how exactly Power Server tells the client the licence as expired (I seem to recall the system keeps recording, you're just locked out of listening to the logs). No doubt PSquared rightly wouldn't want to tell us the finer details of this.
I'd suggest that in Powerlog server there is a utility to manage your Powerlog directory file, check this only lists the logs you want - not something old, then point your client at that. I can't immediately recall if you are using Powerlog Lite if you don't get this and you just have to point the client at the 'logger1' (or whatever it is called) directory.
Myriad user since 1998, now custodian of dozens of Myriad,Autotrack, Powerlog and Scoop boxes of many different flavours.