Problems importing mail into WLM

I recently had to back up my emails, clean the system and import the emails back into Windows Live Mail. however, some of the email folders have not imported correctly. Although the sender and subject line etc are correct, when I try to open the actual emails, the body content is identical in every email. for example

email 1

Sender - Joe Bloggs

Subject - Brown Foxes

Body - The quick brown fox jumps over the lazy dog

Email 2 (and beyond)

Sender - Stephen Hawking

Subject - Complete Transcript of my Book

Body - The quick brown fox jumps over the lazy dog

If I go to the backup drive and open the email from there, it's fine. I can even drag it across into the appropriate folder in WLM with no problem. But as soon as I "batch copy" the emails across, they mess up. With over 13000 emails, I don't fancy doing them all manually.

Any Ideas?