Delete Video using c# asp.net

You need to init a KS [Kaltura Session] first:
KalturaConfiguration config = new KalturaConfiguration(partnerId);
config.ServiceUrl = "http://www.kaltura.com";
KalturaClient client = new KalturaClient(config);
String secret = null;
String userId = null;
KalturaSessionType type = KalturaSessionType.ADMIN;
int partnerId = null;
int expiry = null;
String privileges = null;
ks = client.SessionService.Start(secret, userId, type, partnerId, expiry, privileges);
client.setKs(ks);

of course, input the correct partner ID and admin_secret. You can find them in KMC under the integration tab.