...It might have been deleted.
I am using Outlook 2007 with Windows 7 Home Premium. I lost my Send button two days ago and got it back by reinstalling Office and running scanpost.exe. I have 5 email Accounts set up under Account Settings, but system will only recognize one account. In fact, I get the captioned error message set out above when I try to set any of the addresses as default accounts in Account Settings/E-mail Accounts. I have removed and reinstalled all 5 of them and confirmed through Mail Setup that they are active.
Each account is set up with its own signature.
When I try to write a new email, or forward or reply to an email, the system defaults to one of the addresses which isn't even the one currently set as default in Account Settings, and the system does not insert that account's email signature, but yet another account that the system claims does not exist.

I'm grateful to have email back, but sending emails to my clients from random addresses and with random signatures doesn't do a lot for my credibility. Any help?