major issues with master fader plugins and PT

[satchvai]

Hi guys...I'm running Pro Tools LE 7 with MBOX 1 on a Dell XPS 600. 3.0 Gighz Pentium D dual core, 2 GB ram, etc.. Anyway, tracking and recording is working fine, but lately whenever I use plugins on the master fader track (a multiband limiter C4, master EQ, L2 maximizer, etc...) I get the error message that an "access violation occured." Sometimes I also get a microsoft visual C++ error. Again, this is only when i do anything with the master fader. I have the cpu usage meter open, and I'm never anywhere close to the max. Sometimes, Pro Tools will just close out of the blue or my screen will repeatedly fill up with error messages. I don't know what the deal is here,but I just paid a lot of money to upgrade my setup (new computer, samson monitors, dual monitor display, etc...) What do you think the problem is? What can I do??