DHCP Server does not lease addresses and when try to access Address Lease it gives the "MMC cannot initialize the snap-in error" message

Hello All,

One of our customers has deployed a Windows Server 2008 R2 DHCP server and from few days it does not lease addresses. When i try to access Address Lease it gives "MMC cannot initialize the snap-in error" message (Screenshot is attached). When I check the event lot it just give a warning - "There are no IP Addresses available for lease in the scope or super scope "Scope Name" but there are enough IP address available to release. 

This customer has set of reserved IP's. The main issue is when customer assign a reserved IP it just assign to the end user but it doesn't automatically assign available IP to end users. I have restarted DHCP Server and client Services. DNS is resolving without any issues as well.  As the final solution i tried to unauthorized the DHCP server from the AD but it gave me a error message saying "Access Denied" even the account has Enterprise Level permission.

Please Advice

Thanks,

Dilshan