If your RPT file shows error “Warning: special LOD contains 2nd UV set.” then you can try to fix it by using O2 to do the following:

Go to: Surfaces → UV sets

Normally there should only be one UV set in that list (above Add/Delete Active etc…). It should only contain “v Active 0”.

In this case you will have a second one or even more. You just need to click on the UVset that you don't need (clicking on it will set it active) and then “Delete active”.

Second UV set can be in some of your special LODs like Geometry, Fire Geometry, Shadowvolume etc. Simply go through all the LODs, bring up UV Editor and click the 2nd UV set to select it, then use the menu UV Editor → Delete Active to delete the UV set.