Hi! I'd been thru a lots of difficulties linking my application as well, But afte I did it, What I did is in Application details I used combination of :
*Family name , given name, and Date of Birth ( I did'nt use my Application No. or UCI ) It's works for me
* Then in Applicant's personal information you will noticed: Please enter city and country of birth, or passport information. Meaning to say
You can use either one, I Had trouble putting my COUNTRY OF BIrth, What I did Is leave it blank don't put any information in this area , I put 1 space inside of the box of City/ Town of birth and the next box will remain Please SElect
* Passport information will be completely Filled Up
* Evrything will be filled up until to the last section asking HOW many Family members are included in this application. I put 4, (2 children ,myself, and Sponsor) Although in my paper application when I submitted I put only 3 . I hope it will be help.