Hi Ben,
Usually when we use SSO with BILaunchpad/OpenDoc URLs for the non-AD users, we get the error message that the "Account information is not recognized" and sometimes it gives the 500 error(rarely or never) as well.
This happens because we specify "authentication.default=secWinAD" as the default authentication in the web applications so BO tries to log that user in as AD user.
So if you have enterprise users then those users should get the "Account information is not recognized" error and after getting this error they can type their enterprise username/password. You would need to ensure that the option "authentication.visible" is true in the OpneDoc properties file(This file should be in custom folder) so that users will be able to change the authentication type from Windows AD to Enterprise while login.
Non-AD users can use the link "http://IP:IP:IP:IP:8080/BOE/BI/logonNoSso.jsp" to login to BILaunchpad without SSO.
In BO 3.1, we had an option/workaround to deploy a separate web application in such scenarios but this doesn't work BI4.0 onwards since all of the web applications are included in a single WAR i.e. BOE war file.
If the user is already logged into any BO web application(BILaunchpad,OpenDoc etc) then the other opendoc URLs will take the same session and will log that user in.
~SwapnilY