Out of Memory

You will get the dreaded message "Out of Memory" if your TM1 server reaches beyond 2 GB of RAM.
On top of adding more RAM, you also need to add the /3GB flag in C:\boot.ini to extend the available space of the TM1 server from 2 to 3 GB, if you ever need more then you will have to look for a 64bit server.

C:\boot.ini before:

[boot loader]
timeout=10
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows 2000 Advanced Server" /fastdetect
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="restore mode" /safeboot:dsrepair /sos

C:\boot.ini after:

[boot loader]
timeout=10
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows 2000 Advanced Server" /fastdetect /3GB
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="restore mode" /safeboot:dsrepair /sos

This trick will work only for Windows 2000 Advanced or Datacenter Server and Windows 2003 Enterprise or Datacenter Edition.

It is also recommended that you restart your TM1 service daily in order to free up the RAM used from TM1 operations during the day.

http://support.microsoft.com/default.aspx?scid=kb;en-us;291988

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After a RAM upgrade to 3 GB, you might still get the "Out of Memory" message when you are importing a lot of data at once although your server itself is actually using "only" 2.5 GB.
A way to circumvent that limit is to breakdown the import of data:
use SaveDataAll to commit the changes on disk after some import
then use CubeUnload(cube) of the cube that you just updated. That will free some space that can be used for importing further data for other cubes and that space will be used back to load that cube later once someone opens a view from that cube.