Hi,
I have some experience with the C5 platform... I can't read my ECU with the Nefmoto software, but you may have better luck. An MPPS cable will work well with this ECU if Nefmoto fails.
Easiest way to solve your problem is to disable Cat diagnosis in your current flash, then upload back to the car. Happy to help if you can post the file.
Cheers
You can read. The trick is to connect, attempt a read, allow it to fail, then reconnect. Try with 38k baud, and it should work the second time.
OP: memory layout is 29F800BB.