General Errors

The system cannot find the file specified

Be sure you typed your filename correctly, excluding any dashes, periods, etc. If it persists, try typing the file extension as you save it. If compiling with Hammer, check the log for errors; it often will point you in the right direction.
If you have not ran the game that you are making a map for, or if the destination that you are trying to place the final .BSP file in does not exist at the time you attempted to compile your map, this error will occur as a result of Hammer lacking the ability to create file folders. This happens to a variety of people, most often when the person receiving the error has recently rebooted their computer after a crash, their computer dying, or a virus or other possible cause of computer data/memory loss. If this happens, all you have to do is run the game you are making the map for, or simply browse to the closest file directory to the one you are trying to put the final .BSP in a file browser, and make a folder named the same as the selected output folder.

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Error opening mapname.bsp

The compiler can't find the .BSP file for your map or it's corrupted. Probably the .BSP wasn't created by Vbsp because of an error. If not check the pathname.

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SteamStartup() failed

SteamStartup(0xf,0x12eac4) failed with error 1: The registry is in use by another process, timeout expired
Try recompiling or restarting Steam.

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WARNING node with unbounded volume

This occurs when some part of your map is touching, or is out of the hammer map grid. Move away from the edges of the grid, then compile. Error should be resolved.

BSP (vbsp.exe)

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**** leaked ****

The most common compile error. You have at least one leak in your level. The inside of your map isn't properly sealed to the outside ("void"). Load the pointfile in Hammer. A red line that starts at the specified entity will go through the leak at some point. Follow it in 3D view, seal the leak and recompile.

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Brush XXX

WARNING, microbrush
A brush is too small to be compiled (usually smaller than 1 Hammer unit). Search for the brush with the number specified. Delete the brush and recreate it in a bigger scale.

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Brush XXX

FloatPlane: bad normal
A brush has an unnecessary vertex on a "flat" plane. Probably a result of using the Vertex Tool. Search for the brush with the number specified. Use the Vertex Tool again to fix it by merging the unnecessary vertex with another.

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Can't find surfaceprop for material, using default

There is a texture in your map that doesn't have a material surface property. Probably you used a "model" texture on a world brush. Use the replace texture dialog, search for "model" in your used textures and replace them by others. If you use custom textures make sure they have a $surfaceprop value.

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Errort

displacement found on a(n) (entityname) entity - not supported
There is a brush entity in your map that has a displacement. Displacements may not be brush entities. Search for a brush entity with a displacement on it and remove the displacement or move the brush entity back to a normal world brush.

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Error! To use model "filename.mdl" with static_prop, it must be compiled with $staticprop!

There is a prop_static in your level that is using a incorrect physics model. The model will not show up in game. Use prop_physics or prop_dynamic_override instead.

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Error loading studio model ""

There is a "prop_" model in your map using no model or an incorrect model filename.

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Face List Count >= OVERLAY_BSP_FACE_COUNT

There is a surface with too many overlays on it or an overlay that is applied to too many surfaces.
Its also possible that you changed the lightmap scale setting to a low value (1-8) on a large brush with several info_overlays.

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material "" not found

A surface or an overlay uses no texture or an incorrect texture filename.

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Memory Leak

mempool blocks left in memory:
A chronic error that doesn't affect your map. Ignore.

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Bad planenum

The editor did not save the File Correctly - Re-save and compile. This can also be caused by more then one brush overlapping each other - Normally Caused by a bad Carve.

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Tried parent

The node in the compile has no parent node - this is very rare, but will most likely be caused by vertex manipulation errors passing through hammers safe guard. Think of a box but the whole box is only one side.

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XXX with splits

The brush face has been split, and is a big no, no. The best way to try and fix it is to look for tiny brush penetrations, such as the tip of a spike on touching the side of a 1 x 1 x 1 brush.

VIS (vvis.exe)

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loadportals

couldn't read filename.prt
Vvis can't find the portal file created by vbsp. Either vbsp didn't create it because of an error (leak?) or vvis uses an incorrect file path.

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Leaf (portal XXX) with too many portals.

There is an area with too complicate geometry. Try to simplify some rooms and corridors and make smaller structures func_details.

RAD (vrad.exe)

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Texture axis perpendicular to face at (XXX, XXX, XXX)

At the coordinates specified there is a surface with incorrect texture values. Try to find the surface and make sure the texture is "aligned to world".

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WARNING: Too many light styles on a face (XXX,XXX,XXX)

At the coordinates specified there is a surface lit by too many "effect" lights. This includes lights that have a name (which compiles both on and off status so you could switch them) or a light using effects like flickering. Remove some of them, disable flickering effects or make sure they don't have a name.