Credit to Sarah Hall for this one......
If you have an entry in your SystemOut.log file for Portal which looks like "File not found: /v1.9/dojo/nls/dojo_en.js". This is due to RAD trying to load tags into JSPs that are no longer needed in Portal V8.5. To resolve this, your developers need to remove from their JSPs this series of JSP directives:
Basically, dojo loads as a part of the theme. These JSP directives for a subsequent dojo load that is no longer needed. So, in every JSP that you have (that is created on RAD), find and remove these 4 directives and re-deploy.