Out of variable memory alert in iPhone
To isolate the issue, you can place the device in Airplane Mode and perform a normal slide to shutdown.

When the device reboots, you will have a controlled platform to test. Third party apps will not run until you launch them and Apple's sync services will be  prevented from downloading new data and potentially triggering a memory error.

You will quickly see if it's the OS that is complaining or some app in the background as you run things offline.

This is a fairly obscure error, so you'll want to check that there's some space on the filesystem when you restart the phone. Feel free to edit your question with more details if this alone doesn't resolve the issue for you.

I'd recommend making 500 MB of free space by deleting un-needed apps with no data to back up or deleting some songs if you have no apps to space. Some programs need more room to run, and you might even have several gigs free so it's some other cause that results in the dialog message. In that case, you'll have to pay attention and start things one by one to track down the process that is placing that error on your device.

Also - review the backup article below to be sure you understand what is backed up and what might be lost when you restore things. The over the air update isn't intended to erase anything, but if your device isn't working properly there's no guarantee you will have everything after an update.


http://support.apple.com/kb/HT1766