Outlook 2010 cannot send from additional Exchange account

I have a client who cannot send new emails from an additional Exchange account on one particular computer. Replying to an email in the inbox get sent fine.

Attempting to send new emails sit in the Outbox with the error message:

Task 'email@domain.com - Sending' reported error (0x8004010F) 
: 'Outlook data file cannot be accessed.'

The user can send from the same account ok on other computers with Outlook 2010, so I don't believe it is an Exchange 2007 issue.

I have tried re-creating the Outlook profile on the troublesome computer but this did not help.

Any ideas out there?