First of all, I don't have the 770, but do have the 820.
What I have found is that the error code/pictures don't always align with the problem that is referenced in the manual. Annoying, but it is the truth!
Agree with Mermaid ... turn the machine off, and see if the machine resets and all is seemingly good again. That being said, it can do damage to the machine, specifically the timing. Hopefully not! So for the next while just be aware of how your machine is working.
Good Luck!