I just booked ORD-IST in business with Aeroplan and I'm not having any luck selecting my seat with TK. I tried both the app and TK's website with the TK PNR and 014 ticket number and get this same error message in both:

Dear passenger,

This reservation cannot be viewed due to the sales channel in which it was formed.

You can apply to the channel where you have made your reservation to make a transaction.