I've put my store into Maintenance mode till I can get this fixed...I changed the return url to https://www.havendesignz.com/store/checkout_process and had a customer test it for me, and Paypal charged her twice! And still didn't process the order...I put the extra log file in that was recommended, and here's some from the latest test:

Code:
Sep 24 2008 3:19 -- IPN PROCESSING INITIATED. 
*** Originating IP: xxx.xxx.xx.xxx  dsl-xxx-xxx-xx-xxx.NSW.netspace.net.au
*** Browser/User Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.16) Gecko/20080702 Firefox/2.0.0.16 (.NET CLR 3.5.30729)

Sep 24 2008 3:19 -- IPN FATAL ERROR :: No POST data available -- Most likely initiated by browser and not PayPal.


     *** The rest of this log report can most likely be ignored !! ***





Sep 24 2008 3:19 -- IPN FATAL ERROR :: Could not find stored session in DB, cannot re-create session as PayPal IPN transaction.

Sep 24 2008 3:19 -- IPN FATAL ERROR :: No saved IPN session data available. Must be an Express Checkout or Direct Pay transaction.
This gives my IP address and not the customer's but is the only one different from any previous logs I looked at, so I don't know what's up with that