No access to time machine backup

I just had my 27" imac replaced under warranty. I used the migration assistant to move everything back over. I back-up daily through time machine and I just went to grab some of my files and there's a red icon. I looked on the first backup I did and on this hard drive and it's like that on that one too! It's like that on every single one. I did mess around with users and removed one that I thought I didn't use. I went to add it back and it says the name is already in use but it's not. What did I do!!!???