O2 sensor - Code 44/45 triggers check engine

I have a 1992 GMC 1 ton crew cab with a new 509 stroker running on propane. Since the install I have had an error 44 triggering the check engine indicator. My propane mechanic has advised that I disregard the error code as my dynamic alternate fuel controller isn't triggering on any faults. I have replaced the O2 sensor without any change in the fault indicator.

Any suggestions would be welcome.

Rick