Another interesting issue: I have an application, which has X number of monitored extension and 20 number of recorders.

Everything works fine when I have:
4 or 20 monitored extension. When I increase number to 90 I lose ability to conference in recorder (using single conference method).

This is the error I'm gettin in OnSingleStepConferenceCallResponse()

e.getError = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><CSTAErrorCode xmlns=\"http://www.ecma.ch/standards/ecma-323/csta/ed2\"><subscribedResourceAvailability>generic</subscribedResourceAvailability></CSTAErrorCode>"

If I decrease number of monitored extensions - it starts working again.

What could be the issue where number of extension matter?

Code is pretty generic, taken from simpleRecord

OnSingleStepConferenceCallResponse(object sender, ThirdPartyCallController.SingleStepConferenceCallResponseArgs e)
{
if (e.getError.Length > 0)
{
Thread.Sleep(1000);
getThirdPartyCallController_OnSnapshotDeviceResponse(sender, lastSnapshotDeviceResponseArgsReceived);
return;
}


OnSnapshotDeviceResponse(object sender, ThirdPartyCallController.SnapshotDeviceResponseArgs e)
{
}


List<ThirdPartyCallController.SnapshotDeviceResponseArgs.DeviceInfo> LocalDeviceInfoList = e.getDeviceInfoList;

for (int cnt = 0; cnt < LocalDeviceInfoList.Count; cnt++)
{
ThirdPartyCallController.SnapshotDeviceResponseArgs.DeviceInfo devInfo;
devInfo = e.getDeviceInfoList[cnt];

int i;

// First thing we want to do is make sure all parties are in a connected state.
// We cannot do a single step conference on a call unless all parties are connected.
// If all parties are NOT connected simply sleep for 1 second and then do another
// snapsot device request.
for (i = 0; i < devInfo.getLocalConnectionStateList.Count; i++)
{
// Of course, there are always exceptions. If the connected state is null then a party who
// was once connected has dropped off. This is OK so just go on to the next party in the call.
if (devInfo.getLocalConnectionStateList[i].ToString() == "null")
continue;

string aa = devInfo.getLocalConnectionStateList[i].ToString();
if (devInfo.getLocalConnectionStateList[i].ToString() != "connected")
{
log.Debug("getThirdPartyCallController_OnSnapshotDeviceResponse sending another because all parties are not connected!");
Thread.Sleep(1000);
serviceProvider.getThirdPartyCallController.SnapshotDevice(e.getDeviceIdAsString, null);
return;
}
}
}

// Make sure we did not get an error. If we did, show the user and bail out
if (e.getError.Length > 0)
{
MessageBox.Show(e.getError);
return;
}

// If we got here then the call must be in an OK state to perform a single step conference.
// We need to save the information in lastSnapshotDeviceResponseArgsReceived. We will then
// request the contents of the display because we use the display name as part of the file name (when
// recording to the pc
lastSnapshotDeviceResponseArgsReceived = e;

//-----------------------------
string extensionToConferenceIn;
// Format the extension we want to conference in
extensionToConferenceIn = lastSnapshotDeviceResponseArgsReceived.getDeviceIdAsString; ;
extensionToConferenceIn = e.getDeviceIdAsString;
extensionToConferenceIn = extensionToConferenceIn.Substring(extensionToConferenceIn.IndexOf(":"));
extensionToConferenceIn = AssignAvailableRecordingThruExtension(GetExtension(e.getDeviceIdAsString)) + extensionToConferenceIn;

// Now attempt to conference in the recorder
ThirdPartyCallController.SnapshotDeviceResponseArgs.DeviceInfo devInfo1;
devInfo1 = (ThirdPartyCallController.SnapshotDeviceResponseArgs.DeviceInfo)lastSnapshotDeviceResponseArgsReceived.getDeviceInfoList[0];
serviceProvider.getThirdPartyCallController.SingleStepConferenceCall(devInfo1.getConnectionId,
extensionToConferenceIn,
Avaya.ApplicationEnablement.DMCC.ThirdPartyCallController.SingleStepConferenceCallParticipationType.Silent,
null);
currentRecordingExtension = GetExtension(e.getDeviceIdAsString);
//-----------------------------

// generate get display event for the extension we are trying to record
GetCurrentMonitoringDevice(GetExtension(e.getDeviceIdAsString)).getPhone.GetDisplay(null);
}
catch (Exception exc)
{
log.InfoFormat ("Exception in getThirdPartyCallController_OnSnapshotDeviceResponse: {0}", exc.Message);
}
}

Most likely given this error "subscribedResourceAvailability" you are out of TSAPI licenses. Check AE Services Web LM it will show how many are provisioned and how many are in use.

Each monitor will take a TSAPI license AND each single step conference that is still active. Thus you may need at least 110 licenses for 90 monitored stations and 20 recorders.