Xbox 360 update blocks unlicensed memory units
If you've got an unauthorised Xbox 360 memory unit, then you might want to think about getting an official one ASAP - the forthcoming software update for the console will render it inoperable.
Xbox Live's Major Nelson posted on his blog that "one of the changes is that unauthorized Memory Units will no longer work with the Xbox 360", adding "If you continue to use an unauthorized Memory Unit after the update, you will not be able to access your stored profile or saved games".
If you have a hard-disk equipped 360 then it's not too big a deal - just shift everything onto your hard drive - but if not then you'll need to buy a licensed unit instead and copy the data across. To know whether it's licensed or not, you need a stamp that says "Licensed for Xbox 360" somewhere on the device or its packaging.