Migration Fortiweb 400C to 400D

Hello,

i need help, at the moment we are using a FortiWeb 400C with 6.00-build0007-180522 and now its the plan to change it to 400D.

I'm saving the full Backup from 400C and try to restore it to 400D (tried with 600-build0007 and  v600-build1102), but i got always the error "Configuration file error".

Its possible to migrate the config from the old to the new one.

Thank you