The error code refers to a memory error. Did you recently upgrade the memory?
I suggest removing the memory and verify that it meets the technical specifications for your iMac. If it does, verify that the metal contacts are clean, then try reinserting it. Sometimes simply reseating the memory cleans the contacts and allows it to work properly. You didn't indicate which model/size iMac you have, however depending on how many memory DIMM's are installed you may be able to remove two of them and carefully swap them into the system until you are able to isolate which DIMM causes the error.
These articles may be helpful:
iMac memory specifications - Apple Support
Install memory in an iMac - Apple Support