Kmail identity problem

Hi,

I've recently installed Kontact on a new machine, with 4 identities each with 
a corresponding email address. 

This arrangement still works well on my older machine.

But on the new machine I  have two problems, which may be linked:

1) on starting a new message the From: dialogue box contains only one email 
address, rather than a drop down box with a choice of 4 identities

2) It's necessary to manually set the sender address corresponding to the From 
address to default to successfully send the email.

Any thoughts on how to proceed would be much appreciated

Cheers
Tony