Random exception on Web service call

Hello everybody,

I have a Web service which works fine in production environment.

But sometimes (randomly) an exception is raised :

à System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)\r\n
à System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)\r\n
à System.Threading.Tasks.Task`1.get_Result()\r\n
à fctSendRequestSynchrone[T](String sRequest, enumHttpMethod eMethod, Object oParams)\r\n
à API.csRestApi.d__0`1.MoveNext()"

Here is my code :

.........
//Here is the line which raises the exception :
fctSendRequestSynchrone<string>(string.Format("logs/{0}/message", _lIdLog), cs.enumHttpMethod.POST, oLogLigne);
.........
//-------------------------------------------------------------------------------------
private T fctSendRequestSynchrone(string sRequest, csRestApi.enumHttpMethod eMethod, object oParams = null)
{
Task otask = fctSendRequest(sRequest, eMethod, oParams);
return otask.Result;
}
//-------------------------------------------------------------------------------------
public async Task SendRequest(string sAction, enumHttpMethod eMethod, object oParams = null)
{
string sResponse = string.Empty;
T oValue;
using (var oClient = new HttpClient(new LogginHandler(_oCnx, new HttpClientHandler())))
{
oClient.DefaultRequestHeaders.Accept.Clear();
oClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
string sRequest = string.Concat(_sUrlApi, "/", sAction);
if (_oToken != null)
{
oClient.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue(_oToken["token_type"], _oToken
["access_token"]);
}
using (HttpResponseMessage oResponse = await oClient.PostAsJsonAsync(sRequest, oParams))
{
if (oResponse.IsSuccessStatusCode)
{
HttpContent content = oResponse.Content;
sResponse = await content.ReadAsStringAsync();
}
else
{
throw new RestApiException(oResponse);
}
}
}
oValue = JsonConvert.DeserializeObject(sResponse);
return oValue;
}

Do you have an idea ?

Thank you very much in advance.

Eric