You might want to try changing your router, i had the exact same experience as yourself, tried everything. Setting the game running in an un-firewalled, DMZ'd machine, making sure the DLLs were registered, turning off UPnP, enabling Ping (to stop fragmenting packets) and also changing my MTU size to also sort out any issue with secure connections.
found the issue was with my router, a Netgear DGN1000 (FW: V1.1.00.41_ww) i swapped to an ancient Speedtouch ST536v6 and voilla, everything worked, on a side note, my flatmate who was having an issues with Darkspore and Everquest and those issues dissapeared too, so i think its a way the Netgears handle TCP/IP connections, and i will be writing an email to netgear and trying to test some different netgear hardware too see if the issue is only with this model or weather its more widespread.
Anyways let me know if this works in the context of your issue and if you try a different router and it clears it up