I run my portals in Medium Trust and I was fighting a similar problem with a 3rd party News Aggregator module. In my web.config, my OriginUrl statement read:
originUrl="" (just two double quotes, essentially NULL string)
I changed this to: originUrl=".*" and the 3rd party news aggregator started working immediately.
Apparently, from some research I've done, originurl is processed as a regular expression. The ".*" allows applications in the portal to make requests to any web destination, local or remote. My understanding is when originUrl="", then it is restricted to the local web site.
Note: settings controlling this may also be locked at the machine level web.config, so you may not be able to adjust this. In addition, if your web server is behind an authenticating proxy like ISA Server, it still may not be able to get outside without creating specific rules.
Also, there are security implications to making changes to this, so you should do some research to see how to best configure this in your environment. I wanted to post this in case it helps others understand what might be blocking these requests to external web servers.
Hope it helps.
Rob