"Your document is locked" is certainly a message but "Your document is locked by X user, Click here to message him to unlock or request a permission change or contact XXXX in case of issue" is much much better.
I believe that the errors that the end user see's demonstrate the quality of your product.. so a Fail Whale is always a better option than an "Unexpected Error" but if the fail whale really gives an information on what to do... would be worth.
An error like this does not help at all....
But a error message like this, can do the trick
So Dev? How do you show your quality of work? Just writing good is not enough... write better error messages.