After much wrangling with the hardware on a CLJ4730 copier trying to fix a 49.4C02 error, which occurred only when scanning to email, it turns out that the sysad had blocked users from manually entering an email address. Only entries from the address book could be used. But the users were not told about this change so they, and I, thought we were chasing a hardware error.
It seems strange to me that manually entering an email address could cause a system firmware error requiring a reboot, rather than just giving a user message that manual entry was not allowed.
Oh, well. Lesson learned.