When you are installing Buddypress, the only plugin you want in your /plugins folder is buddypress itself. Nothing in /mu-plugins either. Your plugins which run on buddypress are causing this error.
I have a few plug-ins running, but without the admin back end working, I can’t deactivate them. Can I place them in a separate folder temporarily without causing even more havoc? i.e. welcome pack, monty spam, wp ban, limited log in attempts, askimet, etc.