Is there any chance you can share that source code (your project) with us?
Are you only adding C/C++ source files to your project, or are you adding a wildcard like "*.*" ?
How many files are in your project?
Do things work correctly for you with the sample C/C++ project? (Project > All Workspaces > Sample Workspaces)
When you say SlickEdit becomes unresponsive, do you mean it is laggy, or is it locked up where you have to kill it using Task Manager? If it is the latter, could you capture a mini-dump of it using Visual Studio, so we could see what it is hung on? If it is just laggy, try Macro > Slick-C Profiler > Start Profiling, then work with the editor for a while such that you see the lags, then do Macro > Slick-C Profile > Save...