https://www.infopathdev.com:443/blogs/greg/archive/2004/08/21/Expressions-of-Dissociative-Identity-Disorder.aspxI uncovered this problem on 2004.08.20 while transferring some work from a form I had created earlier to a similar form I was working on. Af first I thought it was a curious little thing, but didn&#39;t give much thought to it as I was against a deadlineenCommunityServer 2007 SP3 (Build: 31118.962)https://www.infopathdev.com:443/blogs/greg/archive/2004/08/21/Expressions-of-Dissociative-Identity-Disorder.aspx#36745Thu, 08 Jan 2009 04:01:26 GMT033a2e2d-04e2-4a9d-be01-a4634161eefd:36745Ryan Beesley<p>I've run into a similar problem with Infopath 2007 when just moving the field data sources around. &nbsp;The expression validates correctly, but when trying to preview the page you get the unhelpful message:</p> <p>Microsoft Office InfoPath</p> <p>-------------------------------</p> <p>InfoPath cannot open the selected form.</p> <p>-------------------------------</p> <p>OK</p> <p>I am unsure what exactly is broken in this expression, but it has something to do with referencing nodes that are in an optional section I believe.</p> <img src="https://www.infopathdev.com:443/aggbug.aspx?PostID=36745" width="1" height="1">