[ConnorMcLeod]

Too many hats may be.

On a server you can't load more than :

512 sprites / models (plugins + game + map)
512 sounds (same)
512 generic files sch as .wad, .mp3, .bmp (same)

So depending on the map you are trying to load, with the same plugins configuration, some maps gonna load, some gonna crash.

Try to identity plugins that precache files, and remove those you don't need, or remove few hats for example.
You can also remove some plugins in specific maps, read the wiki about how to configure.

About that problem, there are dozen of threads on that forum, so please make a search if you have more questions.