If your Flash CS4 crashes when you try to edit some text object is because there is a problem with the font – it may be corrupted or may contain ambiguous data or there are more than one font with the same name or the font symbol name is identical to the Postscript name of the underlying font, etc.

The crash looks like this…

This can be easily fixed by going to adobe.com/support/flash/downloads.html and download the 10.0.2 Flash CS4 Professional Update.

Numerous bug fixes and improvements were added with this update. Some of them are listed bellow.

• Performance issues when dragging objects on stage, scrubbing the timeline, entering symbol edit mode in large AS 2.0 and AS 3.0 files.
• Performance issues when opening large files or files with many nested symbols.
• Performance issues when working in the library such as scrolling, selecting items in the library, dragging item to stage, editing symbol from library.
• Crash when selecting text field on stage with many fonts on user’s system.
• Text Property Inspector is stuck and some controls on the PI are not drawn with certain fonts on user’s system.
• Crash when creating a text object on stage when there are corrupted fonts.

More regarding the fixes on KB407415 and on Galvan on Flash blog.

Hope this will help you improving your Flex CS4 Professional experience.