Paint won't stick to walls
In order to further my knowledge of Hammer I have started upon a test map to familiarise myself with the various elements. I have figured out how to make a paint dropper, however I cannot seem to get the paint to stick to surfaces (Sticks to objects). I have followed the tip to include a light source in the chamber and it made no difference. I have uploaded the VMF, any help would be appreciated
Go to Map Properties and make sure paint is enabled
[Released] Power Interference
[Released] Rust and Dust (Spotlight Map!)
[Released] Multiportal
Go to the "Map" tab of Hammer and select "Map Properties". Then look for the "Paint in Map" field, change it from "No" to "Yes". Click Apply and see if it works now.
You are using a vertex texture for the floor. Paint won't appear on textures that have the _vertex in its name.
Vertex textures... why are they even there?
I've said it at least 20 times before and I'll probably have to say it at least another 20 times but:
never use textures with vertex in their name!
I'm teaching myself Hammer with the Valve developer wiki and unfortunately they didn't mention that small detail 
Whats wrong with vertex textures (other than the fact that paint doesn't work)?