Iis – Network error when keying in credentials

We have an application. We are using Citrix presentation 4.5 server for publishing the application through IIS.

The application is accessible from inside using the private IP. It works fine.

Whenever we try accessing the application from outside it displays the Citrix username /password page . But when we key in the credentials we get this message

Network Error (tcp_error) 

A communication error occurred: "Connection refused"
The Web Server may be down, too busy, or experiencing other problems preventing it from responding to requests. You may wish to try again at a later time.

We access the application using a public IP on a web browser.

It was working fine for few days and then all of a sudden we started facing this issue.

There are no blocks on the firewall. When I use a packet sniffer on the client end outside , I can see the TCP handshake happening. And then we can see this message HTTP 1.1 service unavailable. I have also noticed that whenever I clear the cache of the client web browser the connection goes through.

Below is the event log

Event Type: Error
Event Source:   Web Interface at c:\inetpub\wwwroot\Citrix\AccessPlatform1
Event Category: None
Event ID:   0
Date:       10/20/2011
Time:       2:17:08 PM
User:       N/A
Computer:   apple
Description:
The description for Event ID ( 0 ) in Source ( Web Interface at c:\inetpub\wwwroot\Citrix\AccessPlatform1 ) cannot be found. The local computer may not have the necessary registry information or message DLL files to display messages from a remote computer. You may be able to use the /AUXSOURCE= flag to retrieve this description; see Help and Support for details. The following information is part of the event: The server name "apple.x.ae" cannot be resolved.  This message was reported from the XML Service at address "http://apple.x.ae:80/scripts/wpnbr.dll".  This XML Service could not be contacted and will be temporarily removed from the list of active services. [Log ID: 370d6bc3].

Event Type: Warning
Event Source:   SQLBrowser
Event Category: None
Event ID:   3
Date:       10/20/2011
Time:       2:15:37 PM
User:       N/A
Computer:   apple
Description:
The configuration of the AdminConnection\TCP protocol in the SQL instance CITRIX_METAFRAME is not valid.