We have an Oaisys server running the following software: Oasis Net Server version 3.3.0, Voice Assistant version 3.3.36, Dial Plan Service version 3.0.14, Level20AI version 3.1.31 and Voice Assistant Ports version 3.3.37. We use it for an IVR. When we call the extensions, the recording plays but there is also a dialtone sound and sometimes the call just hangs up. I had a technician check the system. He said it was not a problem with the phone system, but the IVR. What should I start checking? Thanks in advance for your assistance.