mac mail won't work

Hi,

I can't get mail to work on my mac...it works on my iPad fine, but not on the mac (iCloud email).

I get the message: 'can't send mail with iCloud' - but the status is online, the account is enabled...just really confused.

In the mail 'connection doctor', both the IMAP and SMTP have green lights next to them...

Any ideas???

Thanks,

Nik