Cameras do not work with sprites, since the sprites are displayed by screen coordinates, not with the camera view which is 3D.
The way to follow the main sprite is this: instead of moving your main sprite when the user presses a key, move the whole world around it. It may sound mind-boggling but it's not that difficult actually. It does need a bit of planning, since you need to calculate the screen coordinates of each and every sprite that builds your world. If the world is large, then you may even consider re-using sprites to avoid slowing down the program.
For a practical example, please have a look at the little 2D side-scroller program that I posted in the Dark GDK coding challenges thread:
http://forum.thegamecreators.com/?m=forum_view&b=22&t=150933&p=2
Look at my post from 10th Oct 2009 12:06 and its code attachment. It demonstrates screen scrolling (even handling the special cases so that the player can go to the edge of the world on the first and last screens), re-using sprites, and background texture scrolling.
EDIT: It's possible to implement side-scroller games in 3D as well, so that they look like 2D but they are actually 3D. In that case, cameras will work. It's up to you which solution you choose.
