A trap was received and logged in trapd.log with a message that indicated there was no format for it :" Trap received with no known format in trapd.conf"

but I added the specific trap in the trapd.conf file using the xnmtrap application .
the event exist in the trapd.conf !
im sending the trap using the "snmptrap" command with valid parameters (valid Enterprise ID, Generic trap number, and Specific trap number).

how can i fix this?