Hi Jacob,
When you get that error meesage it usually means you're trying to change the default CONFIG bits for the specific device and that you're doing it wrong. This was a VERY common question on the forum before PBP3 was released. PBP3 changed the way that CONFIGs are handled, to the better.

Now, I see from your screenshot that you're NOT trying to tweak the CONFIG so as long as you haven't manually edited any files (and in doing so messed them up) I'm not sure what the problem might be here. Is it possible that you've edited any of .inc files for the 18F4620 in this case?

I opened the Blink example in MicroCodeStudio, selected 18F4620 in the dropdown, un-commented the ADCON1 line and hit compile - no errors, compiles fine. I'm on PBP3.0.7.4 and I'm using MPASM 5.47 (from MPLAB 8.88). I wonder if it's possibly a conflict with the MPASM version you're using (from MPLABX) but it I really don't know.

/Henrik.