I had just finished a first flight test with the PMDG 737 and Ezdok camera today and when I went to restart fsx I had gotten the "FSX has detected a problem with a third party add-on error" (FSpassangers)

I reinstalled FSpassangers but still the same problem .

 

what can I do to get FSpax working again on FSX?

Welcome to the forum, full names on all posts here please.

I'd advise you to contact the developer of that product for support, I am not aware of anything in the NGX installation that would cause problems but I am not familiar with that product.  If it is trying to load the NGX with cargo and pax then that most certainly is a problem because ZFW can only be adjusted through the NGX FMC.  This is mentioned in the Introduction document as well.