Like I said, it only ever worked on certain hardware. Even if it works on your computer it is recommended that you don't because the effect is not widely compatible.
The issue is that different videocards support different amounts of multitexturing built-in. Blitz can emulate more levels of multitexturing, but doing so precludes mixing multiply blending and alpha transparency. Many people are pushing for him to provide a command to determine the multitexturing capabilities of the users card and turn the effect on/off as appropriate, but in the meantime you're best off simply not doing multiply blending on top of alpa textures.
The issue is that different videocards support different amounts of multitexturing built-in. Blitz can emulate more levels of multitexturing, but doing so precludes mixing multiply blending and alpha transparency. Many people are pushing for him to provide a command to determine the multitexturing capabilities of the users card and turn the effect on/off as appropriate, but in the meantime you're best off simply not doing multiply blending on top of alpa textures.