Pictures will explain this better than words:

And in VHE:

Any ideas?

** Executing...
** Command: Change Directory
** Parameters: C:SierraHalf-Life

** Executing...
** Command: Copy File
** Parameters: "C:Documents and SettingsMattMy Documentsmappingmap.map" "C:SierraHalf-Lifevalvemapsmap.map"

** Executing...
** Command: C:PROGRA~1VALVEH~1toolsqcsg.exe
** Parameters: "C:SierraHalf-Lifevalvemapsmap"

qcsg.exe v2.8 (Jan 31 2000)
---- qcsg ----
entering C:SierraHalf-Lifevalvemapsmap.map
CreateBrush: 0...1...2...3...4...5...6...7...Entity 0, Brush 74: A 'Unknown Class' @(0,0,0) has a coplanar plane at (52, -162, 12), texture AAATRIGGER
8...9... (0)
CSGBrush: 0...1...2...3...4...5...6...7...8...9... (0)
Using WAD File: sierrahalf-lifevalvehalflife.wad
added 3 additional animating textures.
0 seconds elapsed

** Executing...
** Command: C:PROGRA~1VALVEH~1toolsqbsp2.exe
** Parameters: "C:SierraHalf-Lifevalvemapsmap"

qbsp2.exe v2.2 (Dec 28 1998)
---- qbsp2 ----
LEAK LEAK LEAK
1 seconds elapsed

** Executing...
** Command: C:PROGRA~1VALVEH~1toolsvis.exe
** Parameters: "C:SierraHalf-Lifevalvemapsmap"

vis.exe v1.3 (Dec 30 1998)
---- vis ----
1 thread(s)
LoadPortals: couldn't read C:SierraHalf-Lifevalvemapsmap.prt
No vising performed.

** Executing...
** Command: C:PROGRA~1VALVEH~1toolsqrad.exe
** Parameters: "C:SierraHalf-Lifevalvemapsmap"

qrad.exe v 1.5 (Apr 6 2000)
----- Radiosity ----
1 threads
[Reading texlights from 'C:PROGRA~1VALVEH~1toolslights.rad']
[1 texlights parsed from 'C:PROGRA~1VALVEH~1toolslights.rad']

No vis information, direct lighting only.
649 faces
26335 square feet [3792329.50 square inches]
2419 patches after subdivision
6 direct lights
BuildFacelights: 0...1...2...3...4...5...6...7...8...9... (1)
FinalLightFace: 0...1...2...3...4...5...6...7...8...9... (0)

Object names Objects/Maxobjs Memory / Maxmem Fullness
------------ --------------- --------------- --------
models 4/400 256/25600 ( 1.0%)
planes 1550/32767 31000/655340 ( 4.7%)
vertexes 959/65535 11508/786420 ( 1.5%)
nodes 365/32767 8760/786408 ( 1.1%)
texinfos 108/8192 4320/327680 ( 1.3%)
faces 649/65535 12980/1310700 ( 1.0%)
clipnodes 644/32767 5152/262136 ( 2.0%)
leaves 204/8192 5712/229376 ( 2.5%)
marksurfaces 836/65535 1672/131070 ( 1.3%)
surfedges 3147/512000 12588/2048000 ( 0.6%)
edges 1668/256000 6672/1024000 ( 0.7%)
texdata [variable] 1192/2097152 ( 0.1%)
lightdata [variable] 61293/2097152 ( 2.9%)
visdata [variable] 0/2097152 ( 0.0%)
entdata [variable] 1170/131072 ( 0.9%)
=== Total BSP file data space used: 164275 bytes ===
1 seconds elapsed

** Executing...
** Command: C:SierraHALF-L~1hl.exe
** Parameters: -dev -console +map "map"

Could be a Hall of Mirrors, but the pic is a bit dark so I can't see. Is there any wierd stuff going on in that blackness or has that brush just disappeared?

Oooh and look what I just found in your log:

CreateBrush: 0...1...2...3...4...5...6...7...Entity 0, Brush 74: A 'Unknown Class' @(0,0,0) has a coplanar plane at (52, -162, 12), texture AAATRIGGER

Check this tut: (a couple of error messages you had in your report are explained there:)

http://www.snarkpit.com/editing.php?page=tutorials&id=2

I see 2 problems.

a. coplanar plane

b. leak

both of these things need to be fixed before anything else can be done. first of GET ZONER'S COMPILE TOOLS. Honestly, you have been around here a while. there is a very good reason why we recomend these tools. primarily they have very good easy to understand error reporting.

Problem a

a coplanr plane is a brush that has too many verticies in a plane. for instance, if you look at a cube in vertex manipulation mode, it should show you eight vertecies, one for each corner. an example of a coplanar plane is if that cube had ten verticies, with two of them in the same plane with four others. the example below is a two demensional illistration. you do not have to delete a brush with coplanar planes. just vertex manipulate the offending vertices so that they are no longer coplanar with the others, or merge them with the others to go back to a propper cube with only 8 verticies.

A good square

.___.

.___.

A coplanar square

._._.

._._.

Problem b.

there are many ways to find leaks. first, try looking around in hammer for any holes in your map. next load the pointfile in game (after fixing that coplanar plane) and fallow it to the source of the leak ( cmd = "pointfile 1")

finaly, if all else fails, start a process of elimination where you use a big cube of sky brush to cover whole sections of your map, and then compiling to see if the leak is gone. this way you can localize the area of the leak to that which you covered in the sky brush.

oh, and GET ZONER's TOOLS!!

Emphasis added by CCS

you know, you posted this question and answered it in the same paragraph, as i read it, the answer is emphatically "YES"

zoners forces people to map correctly, listen to them, in the end you will benefit more.

my advice, stop making leaks if you don't want to have to look for them.