WEAPON MODELLING - TEXTOOL UV MAPPING ISSUES

      So I installed Textools into 3Ds Max and intended to get the UV Mapping and normal map baked within an hour. Unfortunately the issue with my disappearing faces that I thought I'd fixed previously, decided to make a surprise entrance again. I seriously have no idea what to do this time. 

When I apply the checker texture and edit the UV Map (using Textools), the object reverts to a dark grey colour and disappear on the UV Map (as you can see below). 

WEAPON MODELLING - UV MAPPING ISSUES

WEAPON MAPPING - UV MAP ISSUES

I've tried this on several objects.The primitive shapes that make up parts of the weapon are fine, it's just the polygons I'd drawn in myself that are having the problems (the ones that make up 90% of the weapon). If someone could help me with this I'd greatly appreciate it.

I'll browse forums in blind hope for now. Hopefully, I'll get this problem fixed by Monday.

NEXT POST: COMING SOON!