How old/big is your hard drive? May be you need to update it, because this could be a reason why how much vurtual memory do i need popups. Make sure everything about hard drive are ok then you can pass this possiblity, well, a little more, regular maintenance and good using habit will do good to increase its lifetime.Third -- Unreasonable startup or shutdown operation.
Have you ever forced a shutdown operation to your computer with programs running? It's quite bad thing to do, violent and harmful to computer, and yes, it will cause how much vurtual memory do i need error.Fourth - Incomplete or defective third party applications.
Baddly programmed application is likely to be a reason of how much vurtual memory do i need error, when users install or uninstall programes, especially uninstall some applications, some vital or important data/files may be deleted accidently. Next time, when you launch the personal computer or open a program, that file can't be found, then error will pop up windows.