I'm my boss' personal help desk, but that's another story...
He has this consistent problem where he'll create an Outlook 2007 email (HTML format is the default), and while composing it, happily typing away in the email body, he'll suddenly lose the ability to add, edit, or delete text in the body, or set focus anywhere in the body of the email. The email acts just like a sent or received email in that it is not editable.
He thinks maybe he hits an errant key or two when this happens, but I can't find any keyboard shortcut that would cause this issue. Ctrl-Enter would send the email, but it doesn't get sent, so that's not it.
If he saves it as a draft and re-opens it, it's still not editable. His workaround is to then send it to himself, open it, copy and paste into a new email, and finish his composition/editing. This makes him grumpy, understandably.