Citrix XenServer 6.1 guest VM not able to browse (possible TCP issue)

[Manny Aragones]

FW version: 3.18 2011-04-01T23:51:07Z of Flex-10 works good in terms of having a c7000 with a BL460G7 using XenServer 6.1 and having a host machine (Windows 7). Now, if I use the same blade on a c7000 with FW version: 3.70 2012-07-03T21:29:38Z running same config, XenServer 6.1 and Windows 7 as a guest, I get IP and can ping but can't browse the web. 

I have "your browser sent a message this server could not understand" every time I browse the internet. Is there any info available that states what configuration is supported, and/or if any specific drivers must be loaded?