K Framework produces an error in the OCaml backend

Question

I am using the K semantics Framework and running tutorials this is my TEST1.k :

module TEST1-SYNTAX 
import DOMAINS


syntax Fun ::= "add(" Pgm "," Pgm ")"        [strict]
syntax Pgm ::= Int 
            | Fun

endmodule

module TEST1
import TEST1-SYNTAX

    rule add( I1:Int , I2:Int) => I1 +Int I2

    configuration <T  color="blue">
                <k color ="red"> $PGM:Pgm </k> 


    </T>
endmodule

but I get this error when run command Kompile Test1.k:

File "realdef.ml", line 2151, characters 331-338:
Error: This variant expression is expected to have type bool
   The constructor KApply1 does not belong to type bool
 [Error] Critical: ocamlopt returned nonzero exit code: 2
Examine output to see errors.