Did you have a custom macros that auto-inserted closing quotes? You should be able to unbind the commands in Options > Keyboard and Mouse > Key Bindings, and use "Search by key sequence:" for " or ' keys. I'm not sure what is causing the Slick-C stack, but if could post those custom macros here, I can try to figure out what caused the problem and try to prevent it in the future.
Auto-Close is a new editing feature for SlickEdit 2010 that handles insert closing punctuation for parens, quotes, square and angle brackets. If you want to turn off this feature, it can be done per Language or for all Languages in Options > Languages > All Langauges (or specific language) > Auto-Close, Enable Auto-Close.