Problem

If you by accident mis-configured your filter bypasses in /server/filters/*/bypasses the consequence might be that you're not able to access the AdminCentral to fix the problem anymore. This can e.g. happen when you set the class attribute of a bypass definition before properly configuring other attributes.

Solution

If you have a backup of your repository (repositories folder when using derby or external MySQL backup) restore that one in case you didn't change anything else than adjusting the filters configuration.

Otherwise follow these steps: (Caution: please note that this temporarily switches of the complete security system of Magnolia, so be sure to secure your system else wise)
1. shutdown tomcat (ensure all processes are terminated)
2. edit your magnoliaAuthor/WEB-INF/web.xml and comment out the magnolia filter and its mapping
3. copy the file attached (restoreGlobalBypasses.jsp) to magnoliaAuthor directory
4. edit the file, adjust line 26 to match the node name you entered for your filter bypass, e.g. change it to

Content brokenBypass = globalBypasses.getContent("404");

5. save it and restart your tomcat

Tomcat should now start properly, however you're not able to access magnolia at all.
6. in your browser point to http://localhost:8080/magnoliaAuthor/restoreGlobalBypasses.jsp while observing the logs (catalina.out)

If there are no errors you successfully restored the filter configuration.
7. remove the comments previously added in web.xml. This should automatically trigger a web app restart.

Now you should be able to access Magnolia again. Don't forget to remove the JSP file from magnoliaAuthor directory again.

Finally, to add a bypass configuration without hitting that pitfall, first add the properties (e.g. pattern) with an appropriate value and than the class node data. Alternatively you can create bypass configurations just by copying existing ones.