Simplenews unsubscribe link shows a 404 Page
There are many issue thread on simplenews about this issue. 


Simplenews 404 issues


Currently the only supported version of simplenews is version 6.x-1.3 (May 21st 2010).   Most of the issues have patches that are commit to 6.x-2.x-dev and 6.x-2.0-alpha2.  You might want to upgrade.  If you don't, then you will need to apply one or multiple patches to fix your problem.