'x' was passed float from 'y:0' incompatible with expected float_ref
This means that a node in your graph expected to get a variable, but was given a constant instead. This is a message you might see when trying to freeze a graph using graph_util.convert_variables_to_constants. You probably need to add y to the variable_names_blacklist parameter when calling graph_util.convert_variables_to_constants so that it doesn't get converted into a constant. Or, if you're sure you want y to be a constant then you'll need to figure out why your graph contains x that expects it to be a variable; perhaps x can be removed.