I have 3CX v10 licensed version. With 12 internal and 2 remote extensions. All is working well except that we cannot ring one of the remote extension (Linksys SPA-922). The log shows "Failed to acquire SLA slot for DN 506; TODO: Do proper message". The other remote extension is fine. All other extensions are fine. The remote extnsion can make outbound calls, but cannot receive inbound calls. I have checked server settings for SLA_ENABLE and SLA_ONSUBSCRIBE. They are both set to 0. I see this is similar to the thread at http://www.3cx.com/forums/v10-extension-105-there-s-no-free-sla-appearance-20763.html , but I cannot see any resolution in that post. Any help would be much appreciated.