1 Answer

As the message says, you have too many applications open, so there isn't enough memory to start the camera. 

To close running applications, press Alt+Back (Back = the key to the right of the trackball). 

That will show you all active applications. Go to each application, hit the menu key, and scroll down to "Close" option to close the application. 

Once all your applications are closed, you should be able to use the camera. 

Failing that, try a reset (while the phone is ON, take out the battery for 30 seconds, then put the battery back in). The phone will take a little while to restart (you'll see the rotating hourglass) but once it's restarted there will be enough space to run the camera.