Unexpected error when trying to connect Airport Time Capsule base station to network

The old Time Capsule must be plugged from its WAN port.. marked with sunburst symbol to LAN port on your main router by ethernet. (It will only connect the way you are trying to another Airport router)

I select 'Add to an existing network'.

Sorry in Apple terminology the only network is an apple one.. which you are likely not using or the method would have worked. Apple stopped making routers a few year ago.. but it was always rather unlikely every other existing network would be an apple router controlled one.

With the Airport now correctly connected by ethernet.. it can just be a short patch cable. Start the Airport Utility again and select your Time Capsule.

You should be able to fairly easily complete the setup.

I strongly recommend NOT using Apple names.. they are WRONG. Unhelpful, old style no longer suited to SMB networking Apple now uses.

Use short names, no spaces and pure alphanumerics. Passwords same rules but longer.

The utility on the disk is useless.. you must use current one.. always part of the OS now. (There is a manual about setup which reading might prove helpful)

1 The TC is discovered by the utility. Hence Other WiFi Device (1) I turned all my other airports off to make this simple.

TC WAN is plugged by ethernet via a switch to main router, an Asus.. xxyyzz.. main router.. makes no difference what.

2 Click the Other WiFi Device (1).

3 Click your newly discovered TC just like you did before. The Wizard now gathers info.. for a while..

4 Then if there are no other airports it spits out .. create a network.

Type in the new name for wireless and base station name.. you can turn off the wireless name later if you like. Leave it for now. Type in password for both wireless and base station.. Click next.

5 Now it updates the TC and then hopefully completes.

6 Voila your new TC. Click done.

7 Now back at the Airport Utility your TC should appear thusly. BUT it will have errors.. it will need firmware updates.. just click that option. And we can fix anything else. Post a screenshot of where you get to if you run into trouble.

8 To modify any setting click the edit down the bottom of the summary that will appear when you click the TC icon.

The fix for the wireless that you likely don't want or need is to go to the wireless tab and select off.

Click update and you are done!!

Actually there a few other things.. but phase one.. is finished.

There are a few tricks to making a TC work like this ... RELIABLY.

Post back with screenshots if you have issues.