PFC Speirs,
Thanks for the advice.
I uninstalled Arma 3 completely, removed all files from Steam Apps > Common > Arma 3, reinstalled.
Then I downloaded each mod one at a time, then I unpacked them one at a time.
I followed all instructions from the PM to a t.
I'm still getting the same issue, same error.
When I launch Arma 3 without mods, it launches fine with no errors.