could not create merged face I asked a similar question here Part of mesh goes outside but the solution for merging the faces doesn't work on this model. The model is here: 

Basically, the problem with the turtle is in the picture: 

The right leg of the turtle gets distached from the main body of the turtle. I tried joining the faces of the turtle like the recommendation in the earlier question I posted the link to, but I get the error message of "could not create merged face". So I need to find what's causing this.

Also on another note, the left leg while it doesn't get detached from the mesh, it still gets deformed in not a nice way.

Thank you in advance! :)
Instead of creating new faces I used the merge vertices function of blender, here's the final result: 
 
I noticed where the leg of the turtle meets the body of the turtle they are not connected. 
 
All the vertices looked like the second vertex down, on both sides. 

How to fix 

First of all go to where the right leg and body meet, in edit mode. 
From their select one vertex attached to the body. Then select the corresponding vertex on the leg like this: 
 
Once there press Alt + M and finally press A. Once completed do the same to all the vertices, on both sides of the leg. 
If you play the animation now the leg will be deformed, to fix this simply re-set the parent of the mesh to the armature. I did this using automatic weights. 

Happy Blendering!