If you enter a profile ID at the top of that page for any relationship, make sure to NOT use the Go button and scroll to the bottom of the page. There could be another person with a default checkmark, which is already linked to the ID entered above or the original person. Depending on what you are doing, you want to make sure whether a checkmark is needed or not needed for any other people seen at the bottom. If you don't want the person to be linked, as stated, uncheck it. If you select the GO at the top without scrolling, you may be linking a spouse or parent that should not be linked together. It also helps to make sure that you have entered the correct ID at the top if you know the person entered below is related to the ID entered.
