The previous contents of this guide have been found to be over-complicated. In order to fix background maps which show errors about model and brush precaching, you simply need to open the map with GCFScape and extract *mapname*_l_0.lmp to the same folder as the .bsp file. If doing this doesn't work, the old guide, still shown below, should help. If doing this is out of your reach, the old guide most likely will be as well, as it is more complex a process.
NOTICE: THE BELOW CONTENT IS OUTDATED AND IS FOR ARCHIVAL PURPOSES ONLY
Many of you may have noticed some issues with Half-Life mods since the SteamPipe update a short while back. Any mod based on the games has ceased function. Generally, these broken mods can be fixed by changing the contents of the GameInfo.txt file in the root folder of the mod. Some mods, however, don't make it that easy. Lets say you change the contents of GameInfo.txt, and now the game boots, but you're met with a new problem: Once the game starts loading the background map, the game crashes with the message that it's failed to precache either some model or an asterisk with a number after it. Simply put, the background map can't replace any other map. In many mods, the background map was named background01.bsp. This is the same file name as the first Half-Life 2 background, thus the issue arrises. To fix it seems easy enough, change the name of the background. It is a little more complicated, however. Here is how.
First of all, you're going to want to know what to rename. In the maps folder, if there's a file named backgroundXX.bsp, the XX being a pair of numbers from 01 to 07, that's going to be the offending file. If you've found this file, you know what your looking for. Assuming the map is named background01.bsp, you're going to want to rename the following files: (When doing this, you may want to make sure you keep the same number of characters)
In the console folder, you'll also find .vtf files with the same names. Don't change these unless you intend on editing the .vmt files. Once these files are renamed, you're going to want to go to the scripts folder and find ChapterBackgrounds.txt. Open that in a text editor and replace the old name of the background map with the new name. Now, changing the name of the map may break the env maps built in the map. If this is the case, the background will be... very, very ugly. If this has happened, you're going to have to edit the .bsp file some. This is where it's important that you kept the same number of characters as the original file. Open the map file in a text editing program such as Notepad++ and search through for the original name of the map. There will be multiple entries containing the name of the map. These entries all represent folders and the contents of files within the .bsp. Generally, they'll look something like this:
What you're going to want to do is look through for the original map name and replace it with the new map name. If the map has cubemaps, there will be many, many entries, so I recommend using a powerful editor capable of doing it all at once, and all quickly. When doing this, I prefer to search for a bit more than just the map name. For instance, I would search for maps/background01/ and replace it with maps/newbackgrn01/.