Xander975 wrote on Feb 20^th, 2019 at 11:46pm:

But if I were to download the 757-200SF FedEx livery, that installs with the RB535E4 engine variant, and I change the engine variant to either the RB535C or RB5354B engine variant and try to save it, the error does not pop up and the plane loads up with the selected engine variant that I want to use one it. The same goes for all the Pratt & Whitney engine varients. No error popping up.

Does that mean you have a problem with 757-200PCF PCF DHL G-BMRH livery only?