Or you could just wait 5 or 10 minutes and let it sort itself out. Mine does that, at least.
As I understand it..... the router assigns addresses to all the devices that are connected to your home network. Default is that each device gets assigned an address "dynamically." Basically, "on demand". If your network devices don't change much, then the addresses they are assigned will basically just stick to them - while they are connected.
There are all sorts of ways that addresses can get rejigged. For instance, if you take a device off-line (say the MacBook you took to the local Tim's) and then reboot the router, it will reassign IP addresses to the other connected devices. It may reassign the address that the (hypothetical) MacBook was using to a different device at this point. When you connect the MacBook back into the network the first address the MacBook will try to connect with the last address it was assigned.... in this (hypothetical) case an address that has been reassigned when the router was rebooted.
And you get the error message....
In my case, I just leave the devices alone and they sort it out in a few minutes. They don't pay me enough to put on a b&w striped shirt and sent someone off to the penalty box.
I am open to being corrected by an actual network guru.... but this is what I understand, and certainly my real-world observations of our network in action are consistent with my mental model of what is happening.