I am serious about this. CMOs can get corrupt – usually if something with the VSL manager went wrong. In most cases you can trash your CMO. Therefoe use
CTRL + SHIFT + S
regulary. You are using a versioning control system i.e. like subversion? No problem: checkout your file, then always save into new files. Before the commit copy all the versions but the last one into an "OLD" (or however you want to name it) folder. Then take off the version numbers and commit your CMO. This is how I do it – you always have like 10 files between in each commit as backup in case you come back next morning discovering something you didn't saw the night before.
So the golden rule is: don't overwrite a CMO i.e. using CTRL+S – always save into a new CMO.