Unable to add attachments in Mail

For the last few days I have been unable to attach any files to a new message in Apple Mail - either through dragging and dropping or clicking the attachments button and selecting the file. No icon in the message, no warning -- just doesn't take.

This happens when trying to send a message through any of my Mail accounts including Gmail(imap), .mac and an Exchange server.

Anyone have any ideas?

Problem happened while I was running 10.5.1. I have since upgraded to 10.5.2 - no change.

 

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