Graphical Error

[Trineon]

Around the first levels of the SP game, at the map where I sabotage the mining facility, I escape using the tram and thats where the map ends. The next map will not load however, and the game returns to the menu with the following Error message:

 

CMod_LoadBrush Sites: bad shaderNuM: -1

 

Judging from this message I assume its a graphical error. My general specs are:

 

P-IV 1.7 Ghz

256 RDRAM

GeForce 2 MX AGP

and a Windows XP Pro Operating System

 

Has anyone else had this problem? or is it unique to me? Any advice will be graciously accepted for I am desperate

Thanks in advance...