net-zope/zope-exceptions has been bumped to version 3.6.0 and version 3.5.2 has been dropped. Unfortunately 3.6.0 depends on zope-fixers which is python-3 only. Therefore there are no versions left in the tree that are suitable to use with python-2.6. Please re-add a version working with python <3 to the tree.
This bug has been worked around some time ago.