I'm still waiting for full confirmation/PMR numbers from IBM and will post when I get them, but finally discovered what was causing a Cognos Express 10.1 install to fail consistently - I was trying to use an ampersand (&) in the password for the icognosexpress account that is prompted for and gets created during the Cognos Express 10.1 install. The installer does not warn you that this could be a problem, but it certainly appears to a problem based on my testing.
The install will fail at the point of trying to start Cognos Express for the first time, after the content store is created. The error was very unhelpful and indicated the Cognos Express service failed to start. It would leave installed files in place, but all you could really do successfully at that point is uninstall Cognos Express. Manually starting Cognos Express services didn't help - you just get an error about a module not being found.
This appears to be an issue because that password gets embedded, presumably un-escaped, in an XML file at some point and literal ampersands in XML have a special meaning in XML. I have not confirmed this next point, but it's also possible all of these special XML characters would be no-no's for passwords entered during the Cognos Express install:
- & (ampersand - confirmed to be a problem)
- > (greater than)
- < (less than)
- " (double quote)
- ' (apostrophe)
Hope this saves someone some head-scratching & time.