[Xrystal]

Am I guessing right that it only ever happens once per session on first logging in or reloading the UI ?

If so, I am getting that too and I don't use PlayerScore addon ( assuming it is an addon ). I suspect it is just a timing issue with the loading order of the start up events and nUI, if it is calling that function, is calling it at the wrong time.

Try, with just nUI on its own and see if you get the same problem. Just in case it is a conflict between addons.

Edit:
This is the offending line in that file:
local guildName, _, _ = GetGuildInfo(InspectFrame.unit);

As you can see it is expecting an InspectFrame object's unit ID. However, blizzard isn't validating that one exists before trying to use it.. bad programming practise I think rofl. In either case it is the first line of function InspectGuildFrame_Update() which is called when the InspectReady event is triggered.

I did a search through nUI's addon folder and couldn't see an Inspect comment anywhere. Seeing as I recall Scott saying he had removed the inspect option of nUI due to problems it was causing I think I suspect it could be another addon that is playing with the inspect features.