When I change theme I sometimes get the popup
Error: pdhCollectQuery
once every second.

I have a feeling it has to do with some kind of monitoring of the CPU or similar things. But the simplicity theme has CPU monitoring aswell, and there are no problems with it.

where should I be looking?

some modules use external .dll's that some theme owners assume you have on your machine; however I have not heard of this error nor have I ever had it. there is more than one module for cpu usage so the difference between rainmeter and label may just be your problem.

Change the version of Label.dll. Put label 1.95 or more .

thank you