Avast vs Thinkpad Client security 8.2

When Avast 4.8 home is installed on a ThinkPad R500 Vista business with ThinkPad client security version 8.2, the antivirus blocks the ThinkPad fingerpad log on before Windows starts. The normal Windows password logon appears. The password manager works. If I uninstall the virus software the ThinkPad client security fingerprint logon works. This anomaly works with Avira install and uninstall as well. The setup log for Avast seems to recognize that there is an alternative authentication in use and switches to the Windows authentication. Can anyone suggest what can be excluded at the time of boot so that Avast will not block ThinkPad client security?