it means you have a. not much real memory, b. you haven't much space on your hard drive, c. your page file is too small, or d. a combination of all 3. How much free space and how much RAM do you have?
To check virtual memory size:
hold down windows + break
advanced > 1st settings > advanced > change > click custom, set an initial and a maximum size of 1.5 x amout of RAM, and 2 x RAM amount, respectively, click set, click ok.