Problem with Signature - on Vista

I'm having a problem with Signatures on my Vista system. I have Acrobat running on two machines, one is XP Pro (old desktop). Everything on the XP Pro is fine when I sign a document, I just have to put in the password and select the "Reason". On the Vista (new laptop), I have to find the select a digital signature each time I sign, give it a password and then it takes me to the place to attach signature to the document and there are no "Reasons" to select. Is it Vista? I'm running Acrobat 7.1. Any help would be appreciated.