I'm doing some testing on a form including some security testing. One of the things that I ran into was the following error (details shown):

The form uses Universal Data Connections (UDCX). The user I'm testing doesn't have write access to some of the reference lists. When I dug into the issue, I got tons of hits for Kerberos issues and some for the LSA Loopback check issue. However, the issue that I found was that my UDCX file included entries for update as well as reading the data. This was the default UDCX file that InfoPath created – take a look:

<?xml version="1.0" encoding="UTF-8"?>
<?MicrosoftWindowsSharePointServices ContentTypeID="0x010100B4CBD48E029A4ad8B62CB0E41868F2B0"?>
<udc:DataSource MajorVersion="2" MinorVersion="0" xmlns:udc="http://schemas.microsoft.com/office/infopath/2006/udc">
    <udc:Name>Sites</udc:Name>
    <udc:Description>Format: UDC V2; Connection Type: SharePointList; Purpose: ReadOnly; Generated by Microsoft Office InfoPath 2007 on 2009-10-19 at 07:55:36 by DEMO\Administrator.</udc:Description>
    <udc:Type MajorVersion="2" MinorVersion="0" Type="SharePointList">
        <udc:SubType MajorVersion="0" MinorVersion="0" Type=""/>
    </udc:Type>
    <udc:ConnectionInfo Purpose="ReadOnly" AltDataSource="">
        <udc:WsdlUrl/>
        <udc:SelectCommand>
            <udc:ListId>{7159DFE5-D236-472A-81B8-D031EAE14F59}</udc:ListId>
            <udc:WebUrl>http://wss/sites/moc/</udc:WebUrl>
            <udc:ConnectionString/>
            <udc:ServiceUrl UseFormsServiceProxy="false"/>
            <udc:SoapAction/>
            <udc:Query/>
        </udc:SelectCommand>
        <udc:UpdateCommand>
            <udc:ServiceUrl UseFormsServiceProxy="false"/>
            <udc:SoapAction/>
            <udc:Submit/>
            <udc:FileName>Specify a filename or formula</udc:FileName>
            <udc:FolderName AllowOverwrite=""/>
        </udc:UpdateCommand>
        <!--udc:Authentication><udc:SSO AppId='' CredentialType='' /></udc:Authentication-->
    </udc:ConnectionInfo>
</udc:DataSource>

All I did to resolve the problem was to remove the <udc:UpdateCommand/> tag so that the UDC didn't have an update option. That didn't in and of itself resolve the issue -- but as soon as I reuploaded and checked in the UDC files they started working -- the UDCs were not checked in in my connections library.  Doh!