I'm having the same issue described in this forum post.

http://www.redmine.org/boards/2/topics/36850

For some projects I can not edit some wiki pages. Creating new pages works fine though. We recentely migrated from Redmine 1.1.x and it was working correctly before. The logs do not have any error messages.

Applying the suggested patch doesn't not resolve the issue.

Environment:
Redmine version 2.4.2.stable
Ruby version 1.8.7-p352 (2011-06-30) [x86_64-linux]
Rails version 3.2.16
Environment production
Database adapter MySQL
SCM:
Subversion 1.6.17
Git 1.7.9.5
Filesystem

Redmine plugins:
no plugin installed