hi,i am trying to edit a BP and i get this error;An attempt was made to execute a dynamic method callon an initial(NULL-) object reference. The reference must refer to an object. what could be missing?

BP_....AccountActivitiesOV.htm....application BPBT.

what could be wrong? An attempt was made to execute a dynamic method callon an initial(NULL-) object reference. The reference must refer to an object???