Ah! A Swaparoo Problem!
So answer my riddle: Which came first? The Chicken or the Egg?
- You need a chicken to make an egg and you need an egg to make the chicken!
As you likely have two different OS's versions and the format of the drive is likely not compatible with the OS your newer system needs as well. We are faced with a similar problem!
OK, so to break this deadlock you'll need to transfer your stuff to a third device so you can reformat the drive to be reused. So get your self a FireWire HD case if you can (faster), if not you'll need a SATA to USB adapter like this one: Startech 2.5" SATA to USB adapter and you'll need a backup drive to backup your stuff.
So here's the steps:
- Backup your old system (one with the SSD) using Apples Time Machine app
- Take the SSD out and using either a HD drive case or the SATA to USB adapter plug it into your new system
- Using your new system open up Disk Utility and reformat the SSD drive, setup GUID partition table and create a Mac OS Extended (Journaled) partition
- If you don't already have it on your system download the OS installer from the Apps store. Using it install a fresh copy of OS onto your SSD drive
- At the end it will ask you if you want to migrate your user accounts, apps & data. For now we'll say no here
- Shutdown your system open it up and swap out your drives so you have the SSD internally (put your HD aside)
- Now when your restart the system should boot up under the SSD. Go into the prefs and make sure the Startup disk setting is set for your SSD drive. Also finish off installing any OS updates as needed from the Apps store.
- If you want you can also re-install your apps from the App Store so you have fresh clean ones.
- Now after restarting your system, go into the Utility folder and launch Migration Assistant and with your backup drive connected as instructed restore your user accounts, apps (only the ones that you didn't reapply) and your data files from the backup.
Your done with the first phase! Using your older systems SSD in your newer system.
I would recommend you repeat the same steps here to move your newer systems HD into your older system. You may want to review your systems specs here: MacBook Pro 13" 2.26 GHz Core 2 Duo (mid 2009). Jump down to the very bottom to review the OS support entry. Depending on what your newer system had on it you might want to consider upgrading to OS X 10.11 "El Capitan" so you can leverage AirDrop between your systems.