Try modifying your Service like this:
<services>
<service name="mCollectorService.CollectorService" behaviorConfiguration="mCollectorService.CollectorServiceBehavior">
<endpoint address="../CollectorService.svc"
binding="webHttpBinding"
contract="mCollectorService.ICollectorService"
behaviorConfiguration="webBehaviour"
/>
<host>
<baseAddresses>
<add baseAddress="http://localhost:51855/CollectorService.svc" />
</baseAddresses>
</host>
</service>
</services>
And Change your OperationContract
[ServiceContract]
public interface ICollectorService
{
[OperationContract]
[WebInvoke(Method = "POST", ResponseFormat = WebMessageFormat.Json,
BodyStyle = WebMessageBodyStyle.Wrapped, UriTemplate = "Authenticate/{agentcode}/{pin}/{deviceIMEI}/{gpslat}/{gpslong}")]
Authentification Authenticate(string agentcode,string pin, string deviceIMEI, string gpslat, string gpslong);
}
And Call your URL in this way!
http://localhost:51855/CollectorService.svc/CollectorService.svc/Authenticate/YourAgentCode/YourPin/YourDeviceIMEI/YourGPSLat/YourGPSLong
Hope this will help. Thank You!
EDIT: I will recommend you to wrap your request in JSON instead of sending it in the Request URL if you are implementing Authentication mechanism.