Re: I Cannot estabilsh the connection between FortiGate 1000D And FortiGate 3700D
Very doubtful an expired licensing would affected physical connections unless you have firewall policies on the ports with expired UTM policies applied to them.
Are you trying to connect both fgts through a fiber switch or direct-to-direct ports on each fgt? Have you performed diag hardware device info <nic name> on the CLI to see if there is a duplex/speed or any rx/tx errors (do these error counters grow?)
NSE4/FMG-VM64/FortiAnalyzer-VM/5.4/6.0 (FWF40C/FW92D/FGT200D/FGT101E)/ FAP220B/221C