Reports are not listed in ConfigMgr console with Full Administrator rights

Hi folks,
 
I do have a strange issue at a customer´s site. We´ve installed a fresh ConfigMgr 2012 site to be used as a production environment. We´ve done the same for a lab and a transition environment. After configuring the SQL reporting services and adding the RP role to the server, this account who installed the whole site, has local admin rigihts and Full Administrator role permission in the ConfigMgr console, no reports get listed in the console even after 1 hour. Accessing and executing the reports via URL just works fine, so reporting itself seems to be configured correctly. We´ve tested 2 more accounts, gave them Full Administrator in the console and both see all the reports listed. The adminui log file says something about an HTTP error 404  with this problematic account and I´ve no clue, why.
The same effect happens in the lab environment, while in the transition environment, the same account can see all the reports in the console. We´ve checked every setting I could think of, every permission and cannot find the difference between these 3 environments. I´ve no idea why the 2 other accounts work properly while the account used to install everything cannot see the reports in the console, but on the web site.
Any idea what might be wrong with the configuration? 
 
Ingrid