Oracle Message ORA-12052 - cannot fast refresh materialized view string.string

ERRORcannot fast refresh materialized view string.string
CAUSEEither ROWIDs of certain tables were missing in the definition or the inner table of an outer join did not have UNIQUE constraints on join columns.
ACTIONSpecify the FORCE or COMPLETE option. If this error is got during creation, the materialized view definition may have be changed. Refer to the documentation on materialized views.