It seems that you are currently using Magento version 1.5 which contains a small bug, as explained here.
(The bottom line is that "The developers forgot to add the parameter ‘true’ – see in bold below).
The solution is an easy one. All you need to do is as follows:
1. Open the file - /app/code/core/Mage/Api/Model/Server/V2/Adapter/Soap.php
2. Find the line
3. Replace it with the line
->setHeader('Content-Type','text/xml; charset='.$apiConfigCharset, true)
This needs to be done twice in this file.
Once done, log back into StoreYa.com and continue our short registration process – your Magneto API will now be able to import your products into Facebook.