According to the Epson 7700/9900/etc service manual (know it's not the 4900 one, but I don't have that one, and it's going to wind up being similar error codes with the 4900) which you can view at
http://www.costarelli.it/supporto/manuali/Epson%209700/9700_ESP77_79_97_99_SERIES_I.pdf -- I'm sure more searching will turn up a 4900 service manual
On p146 - 1A39
Description: The drive circuit in the Printhead is damaged due to a slant connection of the Head FFC, etc., or the fuse of the Main Board Assy may has blown because of such a wrong connection.
Remedy: 1. Check the connection of the Head FFC to the Sub Board Assy, and correct it if there is a slant connection or the cable is disconnected. If any connection terminal of the Head FFC is damaged, replace it with a new one.
2. Replace the Printhead. (See P.270)
3. If the printer does not recover from the error after trying 1 and 2., replace the Main Board Assy. (See P.228) (The fuse of the Main Board Assy may have blown due to a slant connection of the Head FFC.)
I saw quite a few other people with this error, remedied by reconnecting the ribbon cables. Fingers crossed that moving it jiggled cables loose.