Problems after setting UserVA to 3072

I'm using Vista 32bit with all the latest updates and the latest NOD32 with updates. 4G RAM.

After setting the UserVA to 3072 all the browsers, IE/FireFox/Safari all hang on downloading a file. Hang to the point where I have to reboot the machine.

Setting the UserVA on Vista changes the amount of User Address Space from a default 2048M to the new value, 3072M, decreasing the System Address Space to 1024M.

I am assuming that the virus check happens at this point. If I turn off NOD32 then all is fine for downloading files. If I turn on then I get the hang.

I can run a scan from the Browser after downloading the file.

Any suggestions?

thanks