This error occurs when the DSAB master sees a product it doesn't recognize. This usually happens when the EFIS hasn't been upgraded, and you're trying to detect servos/AP74 with an EFIS running old software.
Does your EFIS show version 5.0 in the SETUP > VRSION menu?
If you have upgraded your EFIS and you still see this error, we should have you selectively take each servo and AP74 offline to see if one of the units is causing the issue.