It should probably go into the MS is guilty forum but .....
Our company recently had a few people succumb to the latest MS Outlook virus/bug/feature and consequently some of them ended up with thousands of emails stuck in the outbox.
situation: you have to delete 16,000 emails from the Outlook outbox. When you select all and hit Delete, nothing happens.
solution: leave the 1st message unselected, select the last 15,999 messages and delete them. Then, you will be allowed to delete the 1st one.
don't ask me why.