CMSimple has a hard time handling "junk data" in your content file. This can get added by copying straight from old versions of Microsoft Word or get added by badly designed System-Protection Software like that from Norton or Zonelabs. Whenever you feel like CMSimple shows weird behavior, check your content.htm file in html view for pieces of code that you don't understand or seem out of place. Its important to have only text between the headlines and not XML-Data or other unknown code.
You should also search for the first HEADLINE in your content.htm and verify that there is nothing above it. Delete everything above it if you find something. Or else it can happen that CMSimple tries to delete your first page every time you hit save!
A good tip if you use copy & paste often is to first copy your text to the windows notepad or to use a tool like "puretext" to purify your text.
Its also recommended to temporarily (while working with CMSimple) turn of software like Norton's Total Internet Security or Zonealarm.
In case you totally messed up you can always restore one of your latest backups.