I have a form library in SharePoint that some people can access and others
can't. The ones who cannot access it get the following error: "This form
cannot be filled out, either because you do not have adequate permissions,
another user has the form open, or the form is open in another program. Do
you want to open a read-only version of this form?" If they click "yes", they
get a SP box (from the site) prompting for their domain user name and
password.  The security level of the template is set to Domain and I'm not
using User Roles.