InfoPath Dev

I have a data connection that is connected to a Data Connection Library on my sharepoint site. The form comes up, the drop down list populates with the names I want. I have the rule set so that my signature textbox will populate with the signature that corresponds with the name selected in my dropdown list. The rule states... Set a field's value: txt_SignatureField with the value @Signature[DDL_Name = @Name]. Yet when I select a name, my text box does not populate. What am I doing wrong?

Another issue I am having is that when I go to preview my form, sharepoint prompts me for my login information 6 times before it connects. Is there a way to keep my form from doing that?

 For your constant login prompt. Modify your data connection, more than likely you've just not ticked the box Save Password. Go through the screens carefully and slowly. It's at the top of one of those screens.

 For your text box, why can't it's default value be the value of your drop down box?

i.e. text box >Properties>default value>"dropdown field".

When I select a name, I want the text box to show their digital signature associated with the name.