Problems since WotLK

Hi there,
on 2.4.3 I was quadboxing without any problems .... it was running great up until now ... everytime I try to open the 4th WoW window it says that I need to check if I had DirectX9 and the lates graphics driver installed and than the 4th window just crashes, this started after installing WotLK.
I also play on privat servers that still run on 2.4.3 (backed up my WoW before patching) and it still works so there's no problem with my Directx or the graphics driver - I guess.

Anyone an idea what might be causing this problem ?? I need my shamans so please help me ^^

-.- never mind ..... just fixed the problem -.- ... the thing is ... the newer the graphics driver the more graphic bugs there are in the game (even on 2.4.3) ... so I just did the most stupid thing you can actually do -.- I just ****ing installed the driver that came with the card (so the oldest one for that card) ..... the result of it is that I'm able to run up do 8 damn WoW windows on my computer now ... I just hate nVidia for stuff like that ... no more driver updates ever again xD