Are you using homegroup for networking? wixed environments should be using the "workgroup" model. It is easy enough to test. create a new network using workgroup. if it works then you can disable IPv6 and kill homegroup
I am using the workgroup model. I currently have IPv6 disabled on the 7x64 machine as well as the XP machine. Still errors out reporting "the specified server cannot perform the requested action"
I also have the 7x64 machine using the Work Network profile.
i have two 7x64 machines, the XP x86 machine cannot access either of them.