Probably the first thing is to be sure "Debug info" is checked when you build the project (under "Project Info" on the "Project" menu).

>I recently restructured my program to have a small exe calling various app files. The app code is located in subfolders under the main program folder. The compiled apps are all in the main program folder. When I SET STEP ON, the debugger tells me 'source not available.' I've tried moving files and setting paths to no avail. Has anyone else had this problem and have a solution? Thanks.