I have wireshark captures of both the Avaya ACE Trainer Application and the custom app. Looks like both respond with just a 0.

=====================================
Avaya Trainer App:
=====================================
POST /CallNotification HTTP/1.1
Content-Type: text/xml; charset=UTF-8
SOAPAction: ""
User-Agent: Axis2
Host: 172.18.0.69:5407
Content-Length: 609
<?xml version='1.0' encoding='UTF-8'?><soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"><soapenv:Body><loc:notifyCallEvent xmlns:loc="http://www.csapi.org/schema/parlayx/call_notification/v4_0/local"><loc:correlator>CallNtf-174233060</loc:correlator><loc:eventNotified><callEvent>Answer</callEvent></loc:eventNotified><loc:callingParticipant>tel:3305236616</loc:callingParticipant><loc:calledParticipant>tel:3586</loc:calledParticipant><loc:callSessionIdentifier>36bf85dc-4705-45ef-818a-122f8b443622</loc:callSessionIdentifier></loc:notifyCallEvent></soapenv:Body></soapenv:Envelope>

HTTP/1.1 200 OK
Transfer-encoding: chunked
Content-type: text/xml
0

=====================================
From the Custom App:
=====================================

POST /CallNotification HTTP/1.1
Content-Type: text/xml; charset=UTF-8
SOAPAction: ""
User-Agent: Axis2
Host: 192.168.17.242:5171
Content-Length: 565

<?xml version='1.0' encoding='UTF-8'?><soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"><soapenv:Body><notifyCallEvent xmlns="http://www.csapi.org/schema/parlayx/call_notification/v3_8/local"><correlator>CallNtf-84109814</correlator><eventNotified><callEvent xmlns="">Answer</callEvent></eventNotified><callingParticipant>tel:3305236616</callingParticipant><calledParticipant>tel:2035</calledParticipant><callSessionIdentifier>9f14a8e7-bc8c-408f-be22-c499767e065e</callSessionIdentifier></notifyCallEvent></soapenv:Body></soapenv:Envelope>

HTTP/1.1 200 OK
Transfer-encoding: chunked
Content-type: text/xml
0

The previous example was from the ACE trainer which apparently uses the 4.0 notificaiton service by default.

Same error from my custom app that is using 3.8:
2013-08-21 17:40:29,961 ERROR-[CALL_NOTIFICATION_V38-192.168.17.242:5171-3][CPDGL-CIE391] (CallEventPublisherTask.java:496) http://192.168.17.242:5171/CallNotification: receiveErrornotifyCallEventV38: com.ctc.wstx.exc.WstxEOFException: Unexpected EOF in prolog
at [row,col {unknown-source}]: [1,0]
2013-08-21 17:40:29,961 INFO-[CALL_NOTIFICATION_V38-192.168.17.242:5171-3][CPDGL-CIE391] (CallNotificationResponseHandler.java:153) Endpoint [http://192.168.17.242:5171/CallNotification] added in faulty list; Subscription will terminate if it doesn't come up within [86400000] millis

I'm getting errors on the ACE Server side when using the call notification 3.8 service. When the service notifies my client of a call, i then get a Unexpected EOF in prolog error once the client responds to the notification. Then followed by the Endpoint [] added in the faulty list; subscription will terminate if it doesn't come up within.

Happens for every call and after 3-4 call notifications, ACE doesn't send a notification. Wait another couple minutes and it starts working again for that subscription with the same errors for each message.

I get the same error regardless if i use my custom client and/or the Avaya ACE Web Services Trainer.

On release: Avaya ACE release 6.2 (6.2.21.30627)

2013-08-21 19:05:28,416 ERROR-[CALL_NOTIFICATION_V40-172.18.0.69:5407-2][CPDGL-CIE243] (CallEventPublisherTask.java:533) http://172.18.0.69:5407/CallNotification: receiveErrornotifyCallEventV40: com.ctc.wstx.exc.WstxEOFException: Unexpected EOF in prolog
2013-08-21 19:05:28,417 INFO-[CALL_NOTIFICATION_V40-172.18.0.69:5407-2][CPDGL-CIE243] (CallNotificationResponseHandler.java:153) Endpoint [http://172.18.0.69:5407/CallNotification] added in faulty list; Subscription will terminate if it doesn't come up within [86400000] millis

Were you able to export the old threads for reference?