One of the most annoying bugs in the game involves losing a stray dog. Once lost, unless you are playing on a PC and use console commands, you won't be able to get an animal follower for the rest of the game, including the Dawnguard animals. I encountered this bug, and I searched for 3 hours to find a possible fix. I was about to give up and just start over, when I found the answer.
If anyone is running into the problem where "you already have an animal follower" even though they do not, go find Meeko if you have not already. Doing his short little quest, reading the journal, and then talking to him will allow you to recruit any animal again.
http://skyrimforums.org/members/nujabe808.12431/
Taken from "My" post on Gamefaqs. i figured i'd spread the word, for people who don't check the site and suffer from the same sort of issue.
"With the arrival of the new Dawnguard DLC i've been wanting to try out the new dog and armored troll companions, but i get the error saying i already have an animal with me, because i lost a stray dog. I searched for hours trying to find a fix for this, but so far i haven't found anything on this subject for xbox/ps3 users, only pc users being able to fix this with console commands.
After a bit of searching for the stray dog i came across meeko's shack, where you can recruit Meeko the dog as a follower after you've followed him inside (I haven't activated this event yet, so he's still by the road). after reading the journal, it let me talk to the dog and recruit him, even though it said i already had a animal with me. I then told him to go back home, and went to try and recruit the new dogs and it worked, I can now recruit the new trolls and dogs on the Dawnguard DLC.
Hope this works and helps people with the same issue. in short: if you haven't activated the meeko's shack quest, then do so and it should recruit him, allowing you to part ways and recruit other dogs/trolls"
Taken from "My" post on Gamefaqs. i figured i'd spread the word, for people who don't check the site and suffer from the same sort of issue.
"With the arrival of the new Dawnguard DLC i've been wanting to try out the new dog and armored troll companions, but i get the error saying i already have an animal with me, because i lost a stray dog. I searched for hours trying to find a fix for this, but so far i haven't found anything on this subject for xbox/ps3 users, only pc users being able to fix this with console commands.
After a bit of searching for the stray dog i came across meeko's shack, where you can recruit Meeko the dog as a follower after you've followed him inside (I haven't activated this event yet, so he's still by the road). after reading the journal, it let me talk to the dog and recruit him, even though it said i already had a animal with me. I then told him to go back home, and went to try and recruit the new dogs and it worked, I can now recruit the new trolls and dogs on the Dawnguard DLC.
Hope this works and helps people with the same issue. in short: if you haven't activated the meeko's shack quest, then do so and it should recruit him, allowing you to part ways and recruit other dogs/trolls"
Here's the link to the guy who discovered at Skyrimforums.
http://skyrimforums.org/threads/already-have-an-animal-with-you-glitch-possible-console-fix.12085/
I'm also editing the Stray Dogs and Meeko wiki pages with this information.