Product:
Cognos Controller 10.3
Microsoft Windows 2008 R2 Server

Problem:
When setup the “database connections for publish to datamart” and click save, you get a error like this:
The ConnectionString property has not been initialized.
An unkown error occurred. Please contact your system administrator for assistance.

Solution:
Ensure that all the steps for upgrade of the Controller/datamart database have been done with the controller DBCONV program.

Open Database Conversion Utility
Select the UDL file and click connect
Select Controller DB or Datamart DB accordingly
Click on Upgrade button, if the current version number is lower than the Upgrade to number.

Please also ensure that the timeout on IIS are long.
http://www-01.ibm.com/support/docview.wss?uid=swg21963432