Fingerprint problem in Dell Vostro 1320

Hi. I have an old Dell vostro 1320 laptop. I installed fedora 16 on it, every thing works good. but I want to login with fingerprint. My fingerprint model is:
Fedora can support this fingerprint and I can enable "fingerprint login" in "User Accounts" Dialog box. But when I want to login, I must swipe finger many times to login, some times I can't login with fingerprint, and some times I must try 8 or 9 timers to login into fedora.:confused:
what is the problem? is this a hardware problem? or fprintd has bug in finger image recognition?:dis:

thanks, and sorry for my poor english.:(