there are a few reasons that it doesn't work...
1. make sure the password you got is correct: this is how to get your password: on your tama go to the icon that looks like a book and go to parents. it will show you your parent, information about your parent yada yada yada. after pressing b a few times it will give you a password. then go to www.tamatown.com and enter the password you got to see your parent.
2. there is a limit of times you can visit your parents so if you've visited them more than 3 times already you can't anymore.
3. hmmmmmmmmm..... thats it i think!