First of all, thank you for sharing your tool with the developper community.
I am initially familiar with Excel VBA development and I duely appreciate to have a step by step debugger such as yours.
I went through the installation instructions and aslo followed the tutorial:
http://technosophos.com/content/debugging-your-php-code-xdebug-mamp-textmate-and-macgdbp-support
On the debugger window, the 2 first pans operate correctly but the bottom pan doas not show the code being executed. I get a simple sentence 'can not open file' instead of it.
Can you help?
Thanks in advance

I had this problem but I think I have a solution for you.
I kept playing around with my sites and putting the php documents in different directories and I found that macdgbp opened the file successfully at certain paths and not others. at first I though this was due to the number of different folders it had to navigate, so like more folders meant not being able to open the file but this was really inconsistent so I checked and realized it was due to spaces in the names of the directories.
I changed my work to my_work and everything worked find.
I'm hoping it gets fixed since I don't want to go through all my directories and putting underscores in.

I can confirm this Bug with v1.5. With other Debuggers like PhpStorm I've no problem with paths withs spaces.

Dupe of bug 224, fixed in master/2.0.