wcf use returning "method allowed"

in slight building initial wcf use i try i "method allowed" explanation.

i've got interface set adult servicecontract operationcontract:

    [operationcontract]
    vacant fileupload(uploadedfile file);

along tangible method:

    open vacant fileupload(uploadedfile file) {};

to opening use i enter
but i "method allowed" error

am i blank something?

code1