It's possible you have some Ada code that tickled a problem in the Ada parser. Is it possible of you to share the project with us? Are the other files (besides Ada source code) in the project? (Makefiles, assembly, Ant, XML...)
Another thing you could do is get a Sample from SlickEdit when it appears to be hung. Go to the Activity Monitor and select SlickEdit and then go to View > Sample Process. You can also collect a sample using Xcode Instruments if you are familiar with that tool.