As i walk around my map, things turn black, and then reappear when i move closer to them, anyone know whats goind on?
The most prominent beig a block that is textured and when i go into the building and look out of the window, it is a large black block 
Screenshots?
I had the same problem in one of the maps I made (i havn't posted it yet though). You can probably see too many polys from looking out that window. I would make it so you don't see so many polys from that window and you should be able to see the box.
Okay, You are using a PROP texture on something that it is not supposed to be used for. the prop textures are actually the SKINS for models. What you need to do to make a fence is use a prop_static and set the [pr]World Model[/pr] to the model name of a fence. i think they are in the wastland or C17 folder in the model browser. I like the Exterior fence ones. Anyway, you can't use the prop texs for non-props. You can prove this by changing the texture (to a non-prop tex) on an object that previously turned black, and it won't anymore. Also make sure it's not a "func wall" or anything like that because sometimes the settings in those will case rendering issues. 
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I hate this problem. On my map, the lighting is fine. But once I add a monitor + camera combo anywhere in my map, i have these 2 "ducts" which totally lose all light.
here's a screen shot of the difference when I just delete the "func_monitor brush.
Does anyone know what this problem is?
None of these suggestions have worked, i am nt using a prop texture, please do not assume that i am sto stupid, i can tell the difference between a skin and a texture, i am unsing one the the base wall textures, as i have not textured the box properly yet.
I cant reduce the polys any more, the place is bare enough as it is.
As for redownloading my SDK i have had several problems and this has solved most of them, but not this one, this also brings my total redownloads to 7 times now, its not funny valve, whats going on?
Its still not working, anyhoo, i may not finnish CS roof, it was a cool idea but im trying to gather up some friends and work on my MOD, ive already got some preliminary work done, and im messing about in XSI EXP for half life 2, all that power at my fingertips and i havent got he faintest idea how to eve load up helperbone, but ive gto some past experence with 3d moddeling so i should be ok after some practice.
Anyhow, i still have not solved this problem but dont think i will. I may redo CS roof, but its not lkely, not at the moment anyway.
[addsig]I had this same problem- Replace any textures that have the word "model" in them. Model textures can't be used. (eg. models/props_c17/furniturefabric003a)
The easiest way to do this is to browse your used textures- check the box that says "Only Used Textures" (in bottom left corner of texture browser)- and use "model" as your filter.
Any textures that come up need to be replaced.
Im also screwing around with a point_camera and func_monitor in CS:S. The point_camera doesnt seem to be set up in CS:S but if I copy and past the entity from a map where it does work it seems to create some sort of custom entity and the icon on the map has bill gates pic on it and says 'obselete'. All that said, when I set it up it works! I can see the point of view of the camera on the brush I turned into a func_monitor that I covered in a dev/monitornostatic (or something like that) texture but when I compile it I get a "func_monitor at x,y,z leaked!" error. The only noticable thing im my small map (very small.. created it just to screw around with things like this) is the compiler error saying it leaked and that all my water looks like it's the void.
Eureka! I figured it out... my func_monitor had an origin set to the middle of nowhere. I changed the origin to the actual origin of my func_monitor and cleared up my leak and all my other problems.
