IP 500. SIP Extn to Extn calls fail 486 User Busy

[ukfactotum]

I have recently moved my IP500 Users over to SIP extensions. The problem I'm seeing is the following:
1. Extn1 calls Ext2 directly - call connects OK with full Audio
2. Extn2 calls Extn1 - Extn1 is Busy (486 User Busy) when not the case
3. Assign DDI & set up Incoming Call Route and point direct to Extn1 - Call DDI and User Busy
5. Assign DDI & set up Incoming Call Route point directly to Extn2 - Call DDI and call connects OK

Note:
1. Extn1 has no problem receiving Hunt Group calls
2. Check Extn1 & Extn2 User & Incoming Call Route parameters both exactly the same.

I'm thinking possible IP routing problem but I'm loss.
Has anyone seen this problem before?

Graham

 

[nolanm]

In Monitor, What is the SIP phone status? Are both the phone AND user logged in? I believe I have seen this happen when it only shows the user logged in. If you are using the same user as before, but pointing to a SIP extension, you may need to delete and recreate the user.