Nokia E71 "Memory full, Close some applications and start again"?

[Lina Anne]

I was deleting messages and when I tried to view one. It said "Memory full, close some applications and try again." There are no applications open and this happened today but this was the second time before I thought it was because my inbox was full that's why I was deleting it but when I checked it again. It said that, now I can't view my inbox. Please help? (