TONS of people have this problem and many people find different things that work for them
Try this:
Not mine. Credit goes to the owner.
"1. Logged in with GC Key account.
2. Permanent Residence > Family Class (Spouses)
2. Application Number and Family Name - Copy/pasted application number from email (including the F) and entered PA's last name. If you don't have App Number, use Family Name, Birthday, Place of Birth
3. City of Birth - I entered 1 space (hit spacebar once)
4. Country of Birth - Selected PA's country of birth
5. Passport Info - Did not enter any passport info
6. Other Application Info - Filled out the other application info as per our application and put '2' as the number of members in the application."
Always use the Principal Applicant's info.
If this doesn't work, search the thread for other people's solutions. And keep trying different thing, though I believe there is a limit to how many time you can try to link in 24 hours.
Good luck!