Cannot open migrated library - old pictures on my Time Capsule

There are two problems, Rick:

• Photos cannot open a library on a Time Capsule. It will refuse to open the library, if it is on a volume, that is accessed over the air or has been used for Time Machine backups. To fix this, move the iPhoto Library to your Pictures folder or another external volume.
• The error message "The contents of the iPhoto Library "iPhoto Library" have already been migrated to Photos." is given by Photos, because it can tell by the filename extension ".migratedphotolibrary" that you already have opened this library once in Photos. Change the filename extension of the iPhoto Library back to ".photolibrary" and Photos can open it and create a new Photos Library from it.

Each iPhoto library will be migrated as a separate Photos Library. To switch between libraries, quit Photos, if it is running, then double click the library you want to open in Photos.

On your old mac, did you migrate from Iphoto to Photos (It sounds like, from the error message that you have, and that you are trying to open the old iphoto library). After you had done this, was your mac still backing up to your time capsule? If so, there should be a backup of your photos library.

Can you go into time machine, and look for a "file" called somthing like Photos Library.photoslibrary (Basically anything.photoslibrary.) If so, restore that and try opening it with photos.

Alternatively - if you did a full restore from time machine after getting your new mac, have a look in your pictures folder for anything.photoslibrary.