Vista Ultimate 32 bit Windows 7 Ultimate 64 bit

I've read through similar questions about sharing between Win7 and Vista, but none of them have resolved my issue of not being able to share between Win7 and Vista:

• Connecting to a Vista shared folder from Windows 7
• Networking Windows 7 and Vista
• Enable File sharing in Windows Vista

Previously
I had previously had my Vista and XP system sharing back and forth without any problems. I was able to access the shares without entering a user name / password in the NT challenge prompt (note: account names and passwords were different on the Vista and XP systems).

Currently
I replaced my XP system with a Win7 system. Now, when I attempt to access shares to/from Vista / Win7, I am continually prompted with an NT challenge to enter my credentials.

Things I've Verified/Tried

• Both systems are on the same workgroup.
• Win 7 is using the Home network. Vista is using the Private network. In other words, neither system is using a Public network profile.
• Enabled file sharing with and without password protection on both Vista and Win7
• Tried HomeGroup Connections (win7) with Windows to manage connections and Use user accounts to connect.
• Reviewed too many online articles to count to trouble shoot.
• Set the shares to have full control by everyone.
• Set up the shares directly on the directory and through the share manager.

My Question
How can I enable file sharing between Vista and Win7 without being prompted with a username/password challenge, ever?