also can you confirm you have updated FS to 9.1 as you state you have trouble approaching the USA,
I only have trouble in the New York City area nowhere else (seems to be a memory leak going on somewhere there with the scenery or something else)... As far as FS versions go I'm using FS9.1 as 90% of my other add-ons wouldn't work.
Well I guess my only solution here is to use the PMDG 744 checklist offered here by Dave Leesley (as one can't modify the default 744 option) and turn off the checklist reverence to the 'NAV, Strobe, taxi, and Landing Lights'. With those options turned off in the Checklist Editor FDC runs without issue on top of the PMDG 744F.
I know when i run the checklist when i come to those callouts i get the usual error calls from VCP,like "whoops forgot that one" or "Oh no how did i miss that" but never the error 6 that you describe,this is very strange.
Yes modifying the calls will do the the trick as you described,at least should be ok from now on,