I am currently working in Germany and I will do my master's degree remotely from England. When I asked those at the university where I will do my master's degree, he said that the diploma is equal to the master's degree at the campus. However, what kind of problems do I have in the online master, will it be a problem for me to do a phd or MBA after this master?
This will probably depend hugely on just what university you are doing your master's at.
Für die Anerkennung zum Zweck des Hochschulzugangs, des Zugangs zu weiterführenden Studien wie auch für die Anrechnung von Studien- und Prüfungsleistungen sind die Hochschulen zuständig.
Universities (Hochschulen, so also universities of applied science, formerly known as Fachhochschulen) are in charge of acceptance [of foreign degrees or diplomas] for purposes of acceptance to study or postgraduate programs, as well as of crediting of foreign studies or examinations.
So your best course of action is likely to talk about this directly with any university you are interested in applying to.
It's a good idea to start this process as early as possible. First, because German bureaucracy can be glacially slow. Second, because they might be asking for additional information. Third, because they might answer with something like "no problem, as long as X", and you might still be able to address any preconditions X right now, rather than finishing your master's and having to do X afterwards, potentially losing time.