I am looking for an example where $f:Y\to X$ and $f':Y'\to X$, are both smooth maps of smooth manifolds, but the pullback does not exist. 

**Remarks:**

1) I know [there are examples][1] where the pullback in the smooth category exists, but is different from the fiber product $Y \times_X Y' = \lbrace (y,y') \in Y \times Y'\mid f(y)=f'(y') \rbrace$ (which is always the pullback in the topological category). 

This is **not** what I am looking for, since in this example the smooth pullback (as the space satisfying the required universal property) exists.

2) In any case where the fiber product is a (smooth) submanifold, it is the pullback. Therefore, any possible example must be one whose fiber product is not a (smooth) submanifold. (In particular $f,f'$ [can't be transverse to each other][2]) 
   
3) [In this answer][3] there is a possible way of poving some limits does not exist. Maybe it's possible to use this method here also, but so far I didn't find an example








[1]:http://mathoverflow.net/questions/124311/pullbacks-as-manifolds-versus-ones-as-topological-spaces
[2]:http://mathoverflow.net/a/1067/46290
[3]:http://mathoverflow.net/a/19473/46290