I was looking for info about this for you.
Serial Error is pretty vague, and recommends just restarting because of internal communication errors.
It could be a firmware issue as Bojan says.
There are two firmwares, Cont and Scon, and the Cont board firmware varies depending on whether the model is a 3050 or 3050Q (5 sided spin mirror) or if the unit has an online processor or is standalone.
Some problems. If you ran it on a PowerMac HQRip, life is easy! Otherwise, you need an old beige mac with OS9 or earlier. Then you can use the download program and firmware files.
Sorry I don't recall the details, but there was a dip switch on the CONT board that would have the 3050 power up in the Forced Download mode. Sometimes if you powered up with the MENU button held, it would also come up in the forced download mode. Sorry though, I might be confusing 3050 with Katana, as they are so similar, but I never heard of having to remove ROMs to reprogram them. Yikes! Hats off to them that they got it working!