I just ran into this same problem with a MicroVAX 3100...
No opening banner, no test numbers, no chevron prompt, just
a few error codes.
It turned out I was using the wrong serial port...
After plugging in to the correct one, I got all the
usual stuff plus the same error codes.

So, try a different serial port...
(or possibly, it might still be sending output to the
framebuffer?)

   -Jeff