There is a memory problem on your Blackberry. Are you sure you don't have applications running ? Do you have only 5 ones opened in the application ribbon when you do Alt-Escape ?
You can see how much memory is left by going in the device options, then Status, then the menu button and "Database sizes".
Anyway, you can try to reboot your device. Just open your blackberry, remove the battery, wait for a minute, then plug it in again. You'll then have to wait for about 4 ou 5 minutes before your Blackberry is operationnal.
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