I P Conflict

Yes, but if your NAS is set to a static IP, then it will ignore the IP address handed out by your router and use what it is set for.  That is the likely scenario and why that's not the best way to reserve addresses.  The better method is to reserve the address within the router.  If you cannot do that, then set the static address to somethng well out of the range likely to be assigned by the router, like xxx-xxx-xxx-200.  If you change it, though, remember that anything else you set up that relies on the static address will also need an update.