Nathan,
I configured the external data sources by adding them to a web map and then using that web map to create the OD. So there is no way (that I know of) to change the URL properties. I looked at the web map, it has the URLs with the proper prefix (http:). I may try creating a new OD and adding the external data sources directly to see if that makes a difference.
I will also troubleshoot by removing one feature class at a time.
Thanks,
Greg