Quick question. Did you verify that the first invocation of SlickEdit had indeed completely shut down, or is their a hidden zombie process out there? Try launching slickedit with +new and see if it still crashes.
Question #2: Are you using one file per window or multiple files share window?
If that's not it, just to try to get a handle on this, try debugging SlickEdit under Visual Studio. This might make it possible to catch the error that is causing the immediate exit/crash.
1) Start Visual Studio
2) File > New > Project... Choose {slickedit}\win\vs.exe
3) Project > Properties... Set up the command line arguments as they are when you launch slickedit
4) Debug > Start Debugging [click OK when it complains about no debug information]
5) Watch it crash
6) Debug > Windows > Call Stack
7) Right click, select All, and then Copy, then send the result
If you do not have Visual Studio, you can also do this with windbg which is integrated into SlickEdit
1) Start SlickEdit with a clean configuration vs +new -sc cleanConfig42
2) Debug > Attach Debugger > WinDBG > Debug Executable
3) Make sure to use +new in the argument list
4) Watch it run and then crash
5) Copy the stack from the Call Stack window