The private key for the identity 'paul@*****.es ( 0xCB1EB42F )' could not be found.

I’ve just signed up for mailbox an as usual I mess about I added my own domain and changed the keys and now I can’t send any email at all because this error comes up

The private key for the identity 'paul@****.es ( 0xCB1EB42F )' could not be found.

I have completly removed the domain and it still comes up with the same error and when i re add it is still there .

I can’t send from the default mailbox.org address either as the error above stops it.

Anybody know what I can do to fix this?

Thanks Paul