I have disconnected the battery first but maybe haven't wait enough longer. Maybe it's cause by the seat disconnected too early. I will try to reset the error code.
The strange thing is that I get a seat belt alarm too with no tone. If I or the passenger disconnect his seat belt, I get the error tone after 30 sec. It's maybe related to the same issue.
 I did a search and found that these warnings are often coming together.
I ordered the wrong connector so I haven't been able to connect the K_CAN. When I connect the battery, I can use the seat motors for around 15min but after the driver seat positions stop working. It looks like the issue you had and it could explain why you have been able to test the seats.
-Can you give me the right connector for the K_CAN wires?
(Is it: Socket terminal MQS 0.2-0.35 MM˛/SN 61131383776 ?)