Well I don't have access right now to a working Carbide, but you will need surely the followings:
- load both projects to your workspace
- at the debugger configuration (something like Debug... or Debug settings, I don't remember), there is a "load symbols" options and then you have to select "from all projects in the workspace" or at least tick your two projects.
- sometimes this does not work. You can try to load the symbols at runtime, there will be a "load symbols from" somewhere in the menu system, you have to select your dll binary here.
- try to put a breakpoint at the entry point of your dll
- if you debug on the device ensure that you copy the debug variant of your binaries into the sis
Debugging multiple binaries in carbide is a bit of matter of luck, sometime you succeed sometime you don't as this part of carbide has some bugs. However it is definitely possible, I did it already in the past :)