I had this problem tonight when I was adding a father. I finally gave up on that browser window, went back to the 'child' profile page, selected add Father, entered everything again and it went through with no problem. It may have been a glitch at the time because I had the same problem that it changed my birth and death year to be the year-00-00 since I didn't have anything more than the year. No issues when I started it again though