The texture should have the following:

[texture]
model=RR
texture=un_03
atc_id=1234
atc_airline=1234
atc_flight_number=1234
ui_manufacturer=Boeing
ui_createdby=Captain Sim
ui_type=757-200 RR
ui_variation= United Airlines, 2003 JS
description='757 Captain' \n (c) 2008 Captain Sim www.captainsim.com \n United Airlines, 2003. Free
livery, repaint by John Smith.

I see that the one that you posted has this line: sim=cs757-F.
The "sim" or .air file used by the CS B757-200F with RR engines is sim=cs757-FRR, while the .air file used by the CS B757-200F with PW engines uses the sim=cs757-F.

So I recommend that (1) you use  "Delete Variation" in the ACE to remove the new livery, (2) remove the sim=cs757-F line from the description.text, and (3) add the livery again using ACE.

See if doing all that fixes it. :)