When installing Cognos Express there are some things to remember when it comes to the location of the installation sofware

1.Special characters are not supported in the installation path
Certain extended characters are not supported when specifying the installation path for IBM Cognos Express and its components. Use only 7-bit ASCII characters when specifying the installation path for IBM Cognos Express as well as any of the client software applications provided with each of the IBM Cognos Express products.

2. Installation from a UNC path is not supported
You may be lucky and Congos Express will install and confiure properly. But when you try to install the Cognos Express modules, they all fail. Just uninstall Cognos Express, copy the installation software to a local disk of your server and install Cognos Express again. Now the Cognos Express modules will install properly