You might have encountered out of memory error when you are running your windows operating system. Though specific reasons cannot be found out instantly, you can narrow down to the possible reason causing this error.
When you have a system that has more than 512MB of RAM, then you may experience this problem when you try opening MS DOS or any such program. This is because the Vcache used as cache takes up all the RAM space by mistake and does not leave virtual address for use by other programs. This will occur when you don’t limit the size of Vcache in the system file. For RAMs greater than 512MB, out of memory error message is very common. To fix this, you have to open system.ini by typing sysedit in the RUN prompt. Then locate system.ini and edit Vcache entry as
[vcache]
MaxFIleCache=524288 for limiting the cache.
Sometimes when you are running many programs, you may get this error because the desktop heap in WIN32 subsystem may be depleted. To fix this problem, open regedit by typing it in the RUN prompt. Then locate the key \System\CurrentControlSet\Control\Session Manager\SubSystems. Change the windows string value by adding 256 or 512 in the shared section parameter after the yyyy for Windows NT and 512 after zzzz number for windows 2000, XP or server 2003 operating system.