It means that you don't have enough RAM. When a program runs, it
starts using virtual RAM, but even that is not enough to
support.
Windows will then pop up this error.
Either you set a higher value for virtual RAM, or you get more
physical RAM.
For setting a higher value for virtual RAM, right click on My
Computer and select Properties.
Click on the Advanced tab.
Under Performance, click Settings. A new window will open.
Click on the Advanced tab in the new window.
Under Virtual Memory, click Change.
Select the Custom Size option.
For initial size, type in the amount of physical RAM that you have.
For example, you have 2 sticks of 256MB RAM, this makes 512MB in
total. Put 512MB in that box.
For maximum size, multiply this by two. This is the default size.
You can add more to this if you are facing virtual memory problems.
For example from 1024 to 2048.
Note that this will eat up hard disk space, since virtual memory
uses the hard disk.
Another way would be to use the method stated by Meat Pao (if you
know what can be safely disabled). I wouldn't recommend disabling
antivirus and firewall, unless you practise safe surfing
habits.
Also, clear your temporary files regularly. CCleaner or ATF
Cleaner are both good and free.
CCleaner gives you more options on what to clear, while ATF
doesn't. Also, ATF is only compatible with Windows 2000 and above
machine, while CCleaner is compatible with all versions of
Windows.
