Scenario #5 - Cognos 8 security is enabled, but not configured correctly.
Scenario #4 - The application server has not been configured correctly.
Scenario #3 - The client PC cannot resolve the WSSUrl value inside 'Client Distribution Server' configuration.
Scenario #2 - The client PC is configured to *not* use 'SelectDb', but there is no database connection named 'Default'.
For example, see separate IBM Technote #1345403.
Scenario #1 - The Controller SQL login (for example 'fastnet') cannot read the required information (for example, the 'dbversion') from the Controller database table(s).
Therefore there are a large number of different potential causes: