Did you read this thread? The answer to why your names are not working is already here if you read up some. =)
Pet names must be 20 characters or less in length.
Pet names must consist of letters or numbers only.
Pet names can only be hatched once. If another pet already holds the name you want, like Bobo, Myia, or Lilie, then you have to choose another name that isn't owned by anyone else yet.
The naming box will turn GREEN when you have found a name that is available.
You can also access the Creatu Search, under the Information Menu, and search the site to see if a name has been taken or not.