ok if it's an evaluation process then it could be that you suplly not valid employee that is process variable used to assign first task to. Antoher thing is that since you modified the evaluation process it could be that
params.put("name", "some name".toLowerCase());
"some name" must be know to task service unless you use DefaultUserGroupCallback that accepts all users.
Since you provided logs from client execution it would be good to check server log where task service is running, there are most likely some errors that causing to return incorrect response.
HTH