Hello
You didnt mention but I assume that the switch Aruba 3810M is the DHCP server, right?
First you need to investigate why this message appears. You can use the commands:
"show dhcp-server binding" will show you how many IPs were allocated to clients and if indeed the pool is exhausted
"show dhcp-server conflicts" will show you how many IPs could not be allocated because some clients claim that they are using them. This IPs are not available for allocation.
As a quick fix instead of rebooting the switch you can try to clear the bindings and the conflicts. For example if "show dhcp-server binding" is showing you that all IPs from the pool were allocated but you know that the WiFi clients are less you can try to clear the dhcp-server binding
Switch# clear dhcp-server binding
If you see that there are a lot of conflicts you can clear the conflicts which will make the IPs available again.
Switch# clear dhcp-server conflicts
If the conflicts start increasing again you need to investigate what causes it. Maybe another DHCP server in the VLAN is assigning the same addresses?
If this doesnt help you can also try to disable and re-enable the DHCP server
Switch# conf
Switch(config)# dhcp-server disable
Switch(config)# dhcp-server enable
Not sure but I think this may also delete the configured pools so use this only as a last resort.