There are times where this error appears in our web application, without a specific reason.
'<name>' is ambiguous in the namespace '<namespace>'
This error has the following error code Error ID: BC30560.
One thing you could easily try is to change the value of the batch attribute in the <compilation> element of your Web.config file to false
<compilation defaultLanguage="vb" debug="false" batch="false">
I recently had the ”<name>’ is ambiguous in the namespace’ error appear in a very popular web site that has about 2 and a half million page views per month. It appeared only in the production server, not in the development or the testing server and nothing could make the error go away.
Changing this setting, allowed the application to have a faster first load (by not loading all objects of its dll at once) and made the error go away.