Foren / Cotonti / Support / Extra fields error after upgrade to Siena

I used extrafields via Pageavatar.

After upgrading to Siena en Pageavatar for Siena. My extrafield does't work anymore.

If I go to Admin --> Page --> Add/Edit extra fields
I get: 

An error occured, maybe a wrong URL?
Redirecting...

Is this a known problem?

Added 33 minutes later:

I checked in a fresh install and no problems for Page-avatar nor extrafields

Added 2 days later:

Logged a ticket: http://trac.cotonti.com/ticket/640

Is there a workaround? Or a solution?