Secret Key Needed and Location on Mac Leopard

[emma]

Hello,

I recently changed my harddrive and upgraded to Leopard.  I'm getting
Enigmail up and running again and get the following error message:

Error - secret key needed to decrypt message; click on 'Details' button
for more information

Looking through the forums I think this means I need to copy over my
secret key, but I can't seem to find where this is located on a mac, nor
how to search for it.

Please could someone help me by explaining if with the error message I
received above this is what I need to do and if so, where do I find this
secret key and where do I put it?

Thanks in advance.

Best wishes
emma