Just thought I might update you on my linking status and what worked for me:
I first tried using File number and UCI copied and pasted from the email. Then tried birth place (put the city only), with both 1 and 2 number of applicants, didn't work. I then tried the file number and PA's family name, with birth place "city, state" copied and pasted from IMM0008 form, with 1 for the number applicant. Didn't work! I changed it to two and that FINALLY WORKED!!!
Summary:
File Number and PA's Last Name
Birth place as per IMM0008 (city, state)
Where applicant intends to stay information as per IMM0008
2 for number of applicants [applicant (wife) and sponsor (me)]
Hope this helps! and thanks!