You need to connect with a LiveCycle server.  See here.  http://helpx.adobe.com/livecycle/help/mobile-forms/preview-xdp-forms-html.html

Also verify in Acrobat (Edit > Preferences > Internet) it's using Acrobat/Reader to view PDF documents.

Have you tried reinstalling LiveCycle Designer?  It should then pick up that Acrobat Pro XI is present and use it for Preview.

7.x version also reached end of life on 6/30/2013.  http://www.adobe.com/support/products/enterprise/eol/eol_matrix.htmlCheck if you had a Maintenance & Support contract and if so, you would have a more recent version available as part of the support contract.

They may be encountering a probelm where the Google Chrome, Safari, or Firefox PDF viewer is used instead of Adobe Reader.  See here for how they can set the browser to use Adobe Reader.  http://helpx.adobe.com/livecycle/kb/xfa-forms-firefox-chrome.html

After reviewing the sample PDF's, it was determined that 1 form was saved as Static PDF and the other Dynamic PDF.  The Please Wait... message was displayed by the Dynamic PDF becuase it was openned in another PDF Viewer other than Adobe Reader.  Links to reference:  http://helpx.adobe.com/livecycle...

Can you share that PDF?

Did he receive the "Please Wait.." message as you noted above with the one PDF that doesn't open?

Forms created with LiveCycle Designer are XFA-based forms.

Check the PDF Viewer used in the browser.  See here:  http://helpx.adobe.com/livecycle/kb/xfa-forms-firefox-chrome.html