Bizhub 361 Trouble Code C-3502/ C-3801

Rebuilt a fuser from another machine (same model), and came to replace it but I am getting C-3502 C-3801 trouble codes.
Repositioned thermostat and thermistors, could not find anything wrong on the rebuilt unit. Reset the Fixing counter, no go. Sometimes I might get a print out and it errors again ... it looks like the machine does not like this unit ... Am I missing something?

Thanks in advance!