Strange one, but probably a common fault? It's on an E46 pre face lift
coupe, so I'm not that familiar.

Had eagle eye aftermarket LED rears fitted, all of a sudden started throwing
errors for both rear lights on the dash.

Changed back to oem rear lights, and the error lights are still on. I was
sure fitting the oem lights woukd solve it.

Have checked the earth wire on the harnesses and they look fine.

Any ideas what could be up that would throw the error?

Cheers