Product:
IBM Cognos BI 10.2.1
Windows 2008 R2 server
Client Internet Explorer 8 or 10
Client Windows 7

Symptom:
After change from Cognos BI 8.4 to Cognos BI 10.2.1 on new servers, the clients get a error message inside Internet Explorer when they try to run reports or click on folders inside Cognos Connection.
Click on Delete browser cache from inside Internet Options does not help.

If the user try to run the same report in FireFox from his computer it works.

Error message:
Internet Explorer Cannot display the webpage
DNS error

Solution:
You must manually erase the files in the IE cache.
From the TOOLS menu select Internet Options.
Select the General tab.
At Browsing History click on the Settings button.
Click on View Files button, to see the files inside the Temporary Internet files folder.
Select all files in this folder by pressing CTRL+A
Click on DELETE key on keyboard to erase the files.
Click X to close the directory.
Click OK to close the browser windows that are open.
Exit IE.

Start Internet Explorer again – and surf to Cognos Connection and see if it works better.