Ground connection on the ballasts is very important. Make sure the ballasts are grounded to a good place with no paint under wire terminal.
I recently ran into same problem on my 09' E92. Installed the HPB CanBus HID kit - supposedly no errors. Same as you, I got low beam headlight errors a couple minutes after start-up. They sent me new ballasts on the off chance that the ballasts were bad - still didn't solve the problem.
I even mounted my ballasts directly to the front frame rails + installed the included Ground wire to frame rail correctly.
I was told there was nothing else they could do, so finally I gave up, contacted Grant, & he let me know which lines to code, changed them all to 'nicht-aktiv' and the problem is gone
If you changed all the lines of code for warm/cold bulb check as reported by Grant to 'aktiv' as you state, you actually turned ON the bulb checks - not OFF, so I don't see how the problem goes away for you? You need to change all bulb check values to 'nicht-aktiv'
BTW, you cannot add error cancellors (resistors) to CanBus ballasts - they won't work as the ballasts already have the error cancelling circuit added into their electronics.
So just because a vendor states that the HID kit is 'error free' - doesn't make it so
Apparently some cars are just more sensative than others...