If it works on some PCs, but not on other, my guess is that the setting in Windows for default email client needs to be set. Check the Default Apps module in Windows and verify there which program is the default email application.

Hi David, No that is not the answer. As I said in my post, the default has been set to Thunderbird in all the machines. I am wondering if there is another setting somewhere. I did read that you need to be tunning 32 bit version of Thunderbird, and indeed the Thunderbird version on my machine is 32 bit, but installing 32 bit on the other machines hasn't helped.