Oracle Message ORA-25109 - standby lock name space has illegal character string

ERRORstandby lock name space has illegal character string
CAUSEAn invalid lock name space was specified for the standby database. The lock name space for the standby database can only contain A-Z, 0-9, _, #, $, . and @ characters.
ACTIONChange initialization parameter _STANDBY_LOCK_NAME_SPACE to a valid character string.