how much free memory do you have? to check go to options > status > file free
I don't know how many apps you've installed on your device, but you may be running low on memory with old stored messages and e-mails etc...
try doing this:
How do I free up memory on my device? - BlackBerryFAQ
or this:
http://www.blackberryforums.com/gene...ee-memory.html