Hello Martin,
Thank you for your post.
We can not say for sure what is the reason of Invalid Stream error while Getting Data from Web.
Please submit a ticket here:
http://support.emagicone.com/submit_ticket and provide us with your store configuration file, so we could check the issue more deeply and advise you on this regard.
*You can save you store configuration file at: Store Manager > Preferences(F12) > Database Connection tab > Store Configuration section > Actions... > Save current configuration:
http://screencast.com/t/Hmy0nUDBsHJc
We're looking forward to hearing from you.