Problems on upgrading OS MKI to V26

[arjelee]

I have a MKI nav unit in my E39 540iaT, current version 1-1/72.
When trying to upgrade to V26 (1-1/80) the system says that the OS CD is correct ant starts the upgrade. When the upgrade is about halfway the CD ejects automatically and the system says that it's finished completly and tells me to remove the CD and press OK. After doing this I found out the OS was not upgraded and is still 1-1/72.
I used a good quality CD-R and burnt it at the lowest speed possible (4x) using alcohol 120%.
I also burnt V24 (nero image) wich automatically burnt at maximum, same story here, it was however recognised as a valid OS CD by the system. So I assume burn speed is not so much the issue here.
What am I doing wrong?

Thanks in advance,

Arjen van Leeuwen
The Netherlands