Unus ex Clientibus meis abiit cum suis vivunt SharePoint 2010 environment hodie. Comperimus quod quidam eorum defaltam humus of users non poterant adire domum page. Responditque SharePoint 'Obvius negavit' et solita 'ut aliud signum in user "seu" aditum petenti "responsum.
Cum usus nifty "reprehendo Obvius" munus confirmavit finem users vere have obvius. Tamen, Page non attingere.
Ego post multum mortuorum fines itinera varias donec placuit ad conferat telam partes in fragmentis Page adversus operantes simili Page. Ego mittens per modum mauris addita pagina "?Summa I-«ad paginam. Ita, sed tamquam "http://server / subsite / subsite / default.aspx?Summa I-«.
Haec ostendit mihi Dominus duas partes textus nomine "error" cum a description similis "erroris" in fragmentis Page. Amet in me est, ut c ad tempus.
Et abstuli eas solvit problema.
Quaestio haec vidi et ascendet super haud dubitat de foro poster praeterita instantia, quod satis est proprie posuit. Me: * ego cognosco, * se satis constituere jus 
Deinde tempore, Ego esse magis et minus aperta dubitat.
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Paulus, we have exactly the same issue going on at a client site right now. We have a very simple 3-tier portal on a single site collection in SP2010 Enterprise. Inheritance is currently “on” for all 3 levels. Users in the Members built-in group (contribute rights) can “go anywhere”. If you take one of those users out and give contribute rights directly OR put them into a custom SP group with contribute rights, they get “Obvius negavit,” on default.aspx down on the 3rd level team site. Using the debug mode noted above reveals *no* broken web parts on that page. It seems as if users *outside* of a built-in group only have “limited access” rights. Have you ever seen this before? Full inheritance seems broken. Ideas?
I know this is ancient. Sorry for never responding. Spero te egredientur figuratum.