Depending on when the Ryanair liveries were done, they may have been created for the CS737-100/200 Exterior models.
If that is the case, then I recommend that you copy the texture.cfg, from one of the default CS737-100/200 liveries into the Ryanair texture folders, replacing the original texture.cfg's.

This is what the texture.cfg for the 737-200 Base Pack has in it:

[fltsim]

fallback.1=..\..\CS_B737-200\texture
fallback.2=..\..\CS_B737-200\texture\bump
fallback.3=..\..\CS_B737-200\texture\spec
fallback.4=..\..\CS_B737-200\texture\night

And this is what was inside the texture.cfg of the 737-200 Expansion Model (before they switched to the -200 being the base Pack):

[fltsim]

fallback.1=..\..\CS_B737-100\texture
fallback.2=..\..\CS_B737-100\texture\bump
fallback.3=..\..\CS_B737-100\texture\spec
fallback.4=..\..\CS_B737-100\texture\LM
fallback.5=..\..\B737_800\texture

Hope this helps.