By looking in the server logs, I was able to see that the error "HTTP Web Server: Command Not Handled Exception" was returning in the logs the following error
HTTP JVM: SEVERE: CLFAD####E: Exception thrown
HTTP JVM: SEVERE: CLFAD####E: Exception occurred servicing request for: /xx/xv.nsf/Category.xsp - HTTP Code: 500
HTTP Web Server: Command Not Handled Exception [/xx/xv.nsf/Category.xsp?action=newDocument]
The issue is that the server version is different than the designer version. I'm using a more recent version which has feature that are not compatible on the server.
"The generated page version 8.5.2 is not compatible with the server version 8.5.1, for the page /Category.xsp."
More info on this can be seen here.
https://www-10.lotus.com/ldd/ddwiki.nsf/dx/XPagesPageVersions.htm
http://stackoverflow.com/questions/17318462/http-500-internal-server-error-when-executing-client-javascript-in-any-xpage
Solution is to upgrade the server to the same version as my designer.