I am running Mathematica 10 under Windows 7 (32 bit).
One of my old examples did not run any more under Mathematica 10. After some digging, I found the following buggish behaviour of Animator. Please start with a fresh kernel and then evaluate:
In[1]:= Animator[x, {0, 1}]
Out[1]= Animator[x,{0,1}]
In[2]:= Animator[Dynamic[x], {0,1}]
(* works *)
In[3]:= Animator[x, {0,1}]
(* now works! *)
In[4]:= Animator[x, {0,Pi}]
(* Mma 10.0 not running, message: "The specified setting for the option FEFloatIterator cannot be used". *)
It seems that in Mathematica 10.0 the command Animator[x, {0, z}] only runs when z is an explicit real or integer, but not when z contains a numerical symbol such as Pi or E. In Mathematica 10.1 this seems to be repaired.
But in both versions, the command Animator[x, {0,1}] only runs when first Animator[Dynamic[x], {0,1}] is executed.