What exactly prevents saving your diagram? Is the 'Save' command not available (not enabled)? Or is there an exception when you try to save? (If so, what does it say?)
If all fails, maybe the following workaround helps you:
-
select your entire diagram (Ctrl+A)
-
copy it to the clipboard (Ctrl+C)
-
open a new editor (Ctrl+N)
-
switch to the new editor
-
paste from the clipboard (Ctrl+V)
Now save the diagram from this editor.