Not sure, as I have only a N900. But here it comes (only) to proxy problems. Settings in settings/internet connections/connections/proxy are valid only for app manager and microb, but not globally.

Do you have/need a proxy set in your connection(s)?
If no, forget about that and sorry.

--edit
Oh, and if we are talking about only one internet connection, it does not make sense at all. As then you will always have problems, not only sometimes.
But maybe you referred to different networks, then it could be.