I am using the Windows 7 x64 default IE8 which is IE8-32 bit. I do not use the IE8 x64 version.
On 23-October-2009, I upgraded from Vista SP2 x64 Business to Windows 7 x64 Professional and it is latest version of Windows 7. All updates from Windows Update were also installed after the initial Win 7 upgrade.
I am reasonably confident that the Avira login worked under Vista SP2 x64 Business and with V126.96.36.199 of SP. The issue with Avira user forum and also the issue with TrojanHunter forum started after V188.8.131.52. I have been running SP V4 betas for approximately 10 months. In fact, I purchased a V4 license on 26-December-2008, shortly after I upgraded from Vista 32-bit to Vista 64-bit. Prior to that I was using V3.x.
I hope this helps.
Win10x64Pro- "home built" ASUS ROG Max VIII Ext, I7-6700K CPU, 32 gb RipJaws, 3 monitors, SS 950Pro, 2 SS 850Pro SSDs; Dell XPS 8700 SE/XPS 410/Surf Pro tablet,: RT-AC88U rtr, WD MyCloud ext, MS Office 2016, Norton Sec, MBAM, MBAE, SAS Pro.