An Airframe Avionics Mechanic reports an EMB-145 flight crew could not enter their pre-flight fuel information into the ACARS system from the Control Display Units (CDU). Days later; when the aircraft returned for overnight service; he realized he had installed the wrong type software version of ACARS computer into the aircraft.

Narrative

The flight crew could not enter their pre-flight fuel information into the ACARS system from the Control Display Units (CDU). I deferred both FMS systems and the ACARS system. The plane went on to its destination.Days later; when the same plane came to overnight here for maintenance on the ACARS system; I was preparing to work on a sub-system of the original gripe; when I noticed that our computerized deferred item tracking system had been updated; stating that this plane needed an Engineering Order (EO) in-order to be (considered) post Service Bulletin (SB). That's when I knew that I had put the wrong type (software version) of ACARS computer on this plane.Four days later; I was pretty sure the problem was caused by the ACARS computer; so I looked it up in the EMB-145 Illustrated Parts Catalog (IPC). I noted that a SB was referenced; so I went to the front matter part of the IPC and that SB was not listed; nor was it listed in the advance revisions. I assumed that it was deleted because all of our aircraft are probably post-SB. I knew this plane recently came from ZZZ; where it went thru acceptance inspections after our carrier received it from another airline. I knew it had the latest Central Maintenance Computer (CMC) and EICAS software versions; therefore I used an ACARS computer with the post SB software version. We don't carry any other version besides.Don't assume that something was complied with or accomplished. Use all means possible to assure it was done.