If you use ActiveMQ 5.x that ships with Camel 1.x and you upgrade it to use Camel 2.0 you can get an exception while starting.
The reason is basically that the XML namespace changed in Camel 2.0 as explained below.
When Camel went from an activemq subproject to a top level apache project, they changed the URIs for their xml schemas to reflect this in Camel 2.0.
To fix this, in activemq.xml change all occurrences of:
These will probably occur in the xsi:schemaLocation attribute of the top level beans tag (both) and in the xmlns attribute in the camelContext element (just the first).