BuddyPress

first of all, sorry, english isn´t my native language.

somites, when i come back to my community there come nothing, but a white screen. without any changing or installation of plugins. simply, suddenly white.
i have to go to the adminpanel one time and after this, everything is fine again and working. just one time /wp-admin is enough.
does anyone know why??

ahh by the way: if the blank screen is shown, i tried an other browser, but it´s the same.
there is no diffrent if “I come back” (says: I´m logged in) or not.