I had this problem once. Just delete all files in your DosBox dir and reinstall. I meant to compare the directories but I misplaced the copy and I haven't been able to duplicate the behavior.

i'm using debian, so i can't do that. i tried reinstalling, but same problem. i tried building from the source, but i got a message saying sdl wasn't installed, even though it is. what am i going to waste my time doing this summer if i can't get this to work??

Check that your window manager doesn't use the Ctrl-Fn keys. Many window managers (including KDE's default configuration) use them for their own purposes. In the case of KDE, you can reconfigure them in the control center (Regional & Accessibility -> Keyboard Shortcuts), other window manages probably have a config file somewhere.

problem solved. it was set up to switch to different desktops, but it wasn't switching to other desktops when i had dosbox open. strange.