Tagging a build with subversion assumes that the credentials are known (or
predefined by the current user) in Hudson. This does not work on my machine
(Windows Server). Even if I start tomcat/hudson under my user, Hudson does not
use the credentials stored in the subversion profile.

While this seems to be a bug I would better recommend to add a user/password box
on the tag this build page since it makes sense to run the svn tag (i.e., copy)
command with a configurable user ID (e.g., a release manager).