Cannot find default value for object, in JavaScript HTTP adapter issue in IBM worklight 8.0

Question

I am using Javascript HTTP adapter, one of the procedure is not working always its throwing Cannot find default value for an object error, could you please check the below piece of procedure call as well as used object and help me where I did mistake.

Procedure call:

function details(tag) {
var path = PATH+'upload/save';
var input = {
    method : 'POST',
    returnedContentType : 'application/json',
    path : path,
    body : {
        contentType : "application/json; charset=UTF-8",
        content : tag
    }
};
return MFP.Server.invokeHttp(input);

}

Used Object:
[{"rId":"5957","tId":"1234","imno":"","dirName":"/storage/emulated/0/demo/Data/1234","userId":"guest","count":"5"}]

Response: always 500 and    "successful": false,

Could you please help me why I am getting always can not find default value for object error.