Update 16.04 on raspi


I run Ubuntu Mate on a raspi 3 for two years now.
I run it mainly offline on a sailing boat for navigation.

I tried tp update the OS today. That did not worked.

Since that I can only boot in emergency mode:
"Welcome to emergency mode ...., type "this and that" ... or type ctrl D to continue"

ctrl D works, but it did ot update.
Terminal says: Ubuntu 16.04.6 LTS is running.

Error during booting::
"Failed to start kernel modules"

What is the problem?
Is it not possible to update Mate on raspi3?
I read something like that.

I dont want to copy a new image on the sdCard, because some token I have bought for sailing charts conneted to this pc/OS. If I change the OS/PC the token will not work.

Best Regards