internal server error status code:500

Hi All,
There is some problem i am facing during the call out to EUP. When i am trying to make a call out from sales force i am not getting back the response and it is throwing some error which says internal server error with status code as 500. When i made a call from external rest api tools like Postman and dft i got the response back. Below is the code i used to make the call out from developer console.

// Instantiate a new http object
Http h = new Http();

// Instantiate a new HTTP request, specify the method (GET) as well as the endpoint

HttpRequest req = new HttpRequest();
req.setEndpoint(''http://eupgateway.yahonline.com:8500');
req.setMethod('GET');
req.setHeader('content-type', 'application/x-www-form-urlencoded; charset=UTF-8');

// Send the request, and return a response
HttpResponse res = h.send(req);
system.debug('$$$$$$$$$$$$$ '+res.getbody());