Describe a bit more what goes wrong.

Does the nav recognise the CD-ROM is inserted and commence the upgrade procedure?
Are you waiting long enough? You need to wait up to 6min
Are you keeping the ignition turned on the whole time? First position (radio on) is sufficient
Did you do a verify after you burnt the disc? You should get minimal errors - I tend to get around 10 errors, which has always been OK. If you get hundreds, suspect a bad CD-R
Have you tried different CD-R media? Sometimes the cheap CD-Rs work better than the expensive ones.
Make sure you have aKey CD on hand. If you upgrade >v17, it will ask for a key CD. Note that Key CD image is not readable on a PC.