This error means someone on the island is currently in a menu screen, dialog, or mid-flight. Wait a few seconds, select "check again", and you should be able to fly in.

More information here.

If you get this error, this can mean 3 things:

1 - You entered an invalid dodo code. The island host gave you an incorrect dodo code OR you are entering the dodo code incorrectly. 

2 - You're trying to access multiplayer, either local or online, but there is no open island you can visit right now. If you are trying to visit an island you know is open, contact the host directly.

3 - The gates to the island you want to go to are closed.

If you experience the "please close the window" error, this means someone is trying to leave and you are directly preventing this. In Animal Crossing etiquette, this is seen as rude and can be easily avoided.

When you see this message, it means you have an window open. This means you are doing one of the following: you have your NookPhone open, you are using any NookPhone app, you are in the reaction menu, you have your inventory/pockets open, you are accessing your storage in your home or from a storage shed, you are accessing an ABD, you are accessing the NookStop, you are in the reaction menu, you are typing a message with the in-game keyboard, you are accessing the recycling bin, you are currently writing on the bulletin board, or in dialogue with a villager or NPC.

If you see this message, IMMEDIATLY close any menu that you are using and is open so the person trying to leave the island can do so. Failure to close your window will result in the island crashing.

If you get this error, this means someone left the island with the minus (-) button. In most scenarios during multiplayer, it is seen as rude to leave with the minus (-) button and can easily be avoided by leaving the island directly through the airport and talking to Orville.

This error can also occur if someone is trying to leave the island through the airport while someone else has an open window (see the error above). The person trying to leave will encounter the interference message from Orville. If the person trying to leave keeps the interference menu open while someone else has an open window, after a view minutes, you will see this quietly left message.

After they leave, you will see the "somebody went home" message (see below). This will also result in every current visitor being automatically relocated from wherever they are, back to the airport. Recent progress by island visitors will also be reset. So whatever you were doing before the person left, you will need to do again.

People currently on an island will see this message after someone leaves either with the minus (-) button OR if someone is trying to leave the island through the airport while someone else has an open window. The person trying to leave will encounter the interference message from Orville. If the person trying to leave keeps the interference menu open while someone else has an open window, after a view minutes, you will see this quietly left message. 

After they leave, you will see the "somebody went home" message (see below). This will also result in every current visitor being automatically relocated from wherever they are, back to the airport. Recent progress by island visitors will also be reset. So whatever you were doing before the person left, you will need to do again.

If you see this message, it means a new visitor is actively flying to the destination island. Don't touch the power button or close the game.

If you encounter this error, it means the island you are trying to visit is currently at full capacity. Islands can only hold 7 visitor plus the host, for a total of 8 villagers at once on any given island. 

To remedy this, the only thing you can do is wait until someone leaves the island so you can take their spot. 

If you are on a treasure/catalog/max bells island, you are not guaranteed to get the free spot when someone leaves because their is usually a high demand for the free spot.

If you get this error, various issues have occurred.

They include but are not limited to:

• Someone's Switch died during multiplayer.

• Someone turned off their Switch during multiplayer.

• Someone's internet crashed or turned off during Multiplayer.

• The game crashed or ran into a technical error that is out of your control.
   

If you encounter this error, it means the island you are trying to visit is currently at full capacity. Islands can only hold 7 visitor plus the host, for a total of 8 villagers at once on any given island. 

To remedy this, the only thing you can do is wait until someone leaves the island so you can take their spot. 

If you are on a treasure/catalog/max bells island, you are not guaranteed to get the free spot when someone leaves because their is usually a high demand for the free spot. Just keep trying to fly.

You may also encounter this error while in the in-flight queue. If the island becomes full while you are in the queue, you will see this error. To fix this, you will need to wait until a free spot opens up on the destination island.

This error means the island you are trying to visit has been disconnected from multiplayer. This could be caused by the island host's internet crashing, their electricity has gone out, etc.

You usually see this error if you are flying to someone's island, or you are already on someone's island. This means your own network/internet is unstable. Your Wi-Fi signal strength could be low or you are too far away from your router. To fix this, simply get closer to your internet router.

You also may have internet that is the incorrect NAT Type. NAT is a process that is crucial for your devices to connect to the internet. NAT Types that allow your Switch to connect to the internet are: NAT Type A and B. If you have one of those, your Switch should have no problem connecting to the internet and participating in multiplayer.

If you have NAT Type C or D, you will encounter this error. This basically means your Switch cannot communicate with your network and you cannot engage in multiplayer.

You can check your Nat Type on your Switch by going to: Settings > Internet > Test Connection.

There are also methods you can research to change your Nat Type. Contact your internet service provider or an adult that do so for you. 

You can get this error if your internet connection has timed-out either due to a slow internet connection or a weak wireless signal.

Please refer to this guide from Nintendo on how to fix this error.

Please refer to this guide from Nintendo on how to fix this error.