I just entered this route in the 757 FMC and it looks fine, I have no magenta lines going all over the place like in your image. :-/

The route:

EGLL RWY27R DVR5F.DVR UL9 KONAN UL607 AMASI UM149 DETEV UL603 DINKU UQ305 BIBAG UL605 NEKUL UM747 ENIMA TOSV1E.TOSVI ILS08R LROP

You will notice that I did not go to BALBI, I only went to ENIMA. This was because of the Runway and STAR I selected to land on.

You can download my EGLLLROP757.rt here: https://www.dropbox.com/s/yero50b8jqpmi1f/EGLLLROP757.rt?dl=0

Save it in the FSX\Captain_Sim\navigation\routes folder

Load it into the FMC by clicking on the LSK 3L (beside <SEND on the RTE page), find EGLLLROP757 and click on the LSK beside it.

Then see if you still have the crazy magenta lines on your display (mine doesn't). ;)

NOTE. I downloaded your EGLLLROP.PLN, but I couldn't load it into my 757 FMC, so I created the route in the FMC from scratch.