"You must close all open Dialog Boxes before saving" and believe me there all closed. Now I had this same problem back with Oblivion's CS when I switched to a new rig. I managed to get around this problem by modifying an .ini file for the Construction Set to ignore this 'check before saving.' Thing is a I cant find it for the CK or remember where it was located for the CS. Anyone know?

I'm having the same issue. Hope this can be fixed soon as I'm eager to get started working with CK.

Disabling UltraMon or any other type of taskbar extender worked for me.

Turn on the bAllowUnsafeSaves INI key in SkyrimEditor.ini.

I've been having a save issue when working on a new exterior cell's height-map. When I try to save the terrain texture it says File in use, with a clock counting up. Canceling out of it shows progress in the save, but the File in Use error pops back up, and then the Creation Kit crashes.

Same issue too.

That problem has been solved, by either reinstalling the creation kit (although I did for another purpose) or changing the line bAllowUnsafeSaves INI key in SkyrimEditor.ini. as described above.
I don't recommend creating steep slopes.

are you sure you are not running the CK and at the same time keep open a game session? In this case it won't save ...