Running Out of Memory
From X-Plane Wiki
X-Plane 9 can sometimes fail with the following error message:
X-Plane has run out of video card memory
This usually happens with the video driver cannot allocate enough address space to continue running X-Plane.
The general solution to this problem is to turn down rendering settings, particularly if you have a lot of third party add-ons installed. There are also some tweaks you can make to your operating system that might help.
Tweaks for Windows XP
If you have not already done so, you can set Windows XP to allow applications to use up to 3 GB of memory. This is done by adding the flag /3GB to your boot.ini file. boot.ini lives on the root of your boot drive - you may have to show hidden items in the Windows Explorer to find it. Here is a typical boot.ini with /3GB.
[boot loader] timeout=30 default=multi(0)disk(0)rdisk(0)partition(4)\WINDOWS [operating systems] multi(0)disk(0)rdisk(0)partition(4)\WINDOWS="Microsoft Windows XP Home Edition" /noexecute=optin /fastdetect /3GB
The last switch (/3GB) is the one you must add to allow X-Plane to use 3 GB of virtual memory.
Tweaks for Windows Vista
If you are running out of memory on Windows Vista, there are two things you can do:
1. There is a hot-fix that helps Vista's video memory manager use virtual address space more efficiently; you can read about the hot-fix and download it here:
http://support.microsoft.com/kb/940105|http://support.microsoft.com/kb/940105
2. You can increase the amount of memory X-Plane can use from 2 GB to 3 GB - this is done using the Boot Configuration Data Store. From a DOS prompt, run this:
BCDEDIT /set increaseuserva 3072
This will allow X-Plane to use 3 GB of virtual memory instead of 2.