Through more testing I found that I was getting the invalidPartyException on some calls as well. As I stated before getting the busy signal was because of a race condition that was found and reported to development. Even if we had the exact same versions of Avaya software there are still other factors like OS, and network issues at play. In your case though it sounds like the TWS is working as it was designed to.

Ok, so it looks like that it works as designed - thank your for your help.

Two last things:
1) Is it possible to catch the InvalidPartyException in the client and triggering a busy tone manually from the client side (for example call a pseudo number on the core which is busy or so?).

2) Is there an other solution for our requirements as the Agile Communication Environment. We only need a Click2Dial function which should be adaptable (to implement it in Lotus Notes - Java!) and should signal a busy tone if called party is busy.

1) This might be possible, but the problem is that the call is disconnected once the invalidPartyException is sent back to your application. So the phone is no longer off hook to do anything.

2) Have a look at this document from Avaya support: http://downloads.avaya.com/css/P8/documents/100127025

As I told you below, the Sametime integration is no alternative because we haven't rolled out extensive. But we talk with our vendor about alternative solutions.

For point 1)
Can't we create a second connection to a busy tone directly the first call fails? So if the InvalidPartyException reaches the client it would be catched and the client starts a second call to a pseudo user which is signaling the busy tone.

That would be a workaround for the off hook problem?

If that is something you would like to try that is up to you. It sounds like you could make a call to a VDN which plays hold music (busy tone) for a certain amount of seconds and hangs up.

Hello again.

As our recent tests shows, it seems this would work.
Many thanks for your help.