Two different purposes. Including a reference to the project tells the project where to find this other resource. The "Using..." directive allows for typing shortcuts in your code and can be used in other ways then just saying "Use System.Whatever.Whatever".

>Reply to my own message...
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>Solved the problem - I hadn't included the System.Drawing reference in the project! I'm surprised the reference isn't automatically pulled-into the project when a 'using System.Drawing' reference is detected.
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>Alan