The Server Block is not well formed

Issue:

An error occured whenever the user clicks on a particular Sub-Site "The Server Block is not well formed."

The Reason

While I'm sure a number of scenarios can create this situation. In my case, It was a matter of customization carried out on the Web-parts. Hence It was generating the Error message when the user tries to open the Subsite where the webpart resides.

Resolution:

Goto the SharePoint Settings page by adding _layouts/settings.aspx at the end of the SharePoint Site URL For Ex: https://testserver/sites/testdemo/testsubsite/_layouts/settings.aspx

The following URL would take you to the Site Settings page

Finally perform the simple steps mentioned below:-

1. Goto Look and Feel
2. Reset  to Site Definition
3. Select Reset Specific Page to Site Definition Version
4. Provide the Local url of the page i.e. https://testserver/sites/testdemo/testsubsite/default.aspx
5. Click on Reset
6. Done

By Resetting the Site Deinition, It would restore the Site with default settings and close all the Webparts and then the user was able to open the Site.

Thanks