I have 3CX Version 3 and I (luckily) backed up the database and upgraded to Version 5 RC2. It then did the following: - Incoming calls from VoipTalk (SIP Provider) failed intermittently (works after reboot but fails after 5 minutes later) but Sipgate worked perfectly. :x - Calls between extensions failed. I uninstalled the software, reinstalled it and added two extensions, configured on two PCs and test calls and I get an error. It did respond as previously. I then downgraded to Version 3 and it sorted the problem out! I am now back to Version 3 but I WANT to get through to Version 5 as it has fax capabilities which I need! Btw, I am installing this very soon at a client site. I am installing this software on a Server with Windows 2003 Server x64. Please help me get over this ordeal as soon as possible.