SharePoint:WebPartPageUserException This page has encountered a critical error

遇到以下webpart莫名錯誤，很常見吧。通常用戶是直接刪掉，知道緣由的不算太多。

解決辦法(Solution)：

Usually, This error caused by wrong entries under <SafeControl> section in web.config. Remember, Web.config is case sensitive. Instead of "TypeName" if you place "typename" it could lead you to above error!!! Check for Invalid entries in web.config file in order to avoid this error.

Other possibility is: If the site template you are using is not registered as safe in web.config or the feature which you try to install does not register the safe entries may cause this issue.

Solutions:
In my case, Restoring web.config from earlier backups solved this issue. 
If you don't have web.config (You are a bad SharePoint Administrator!) Take every entry out of <SafeControl> section, and try adding them one by one. Stop and find the culprit!

from:http://www.sharepointdiary.com/2012/01/fix-for-this-page-has-encountered.html