[OS X TeX] Missing $ inserted in a "variations" environment

[ewan.Delanoy at math.unicaen.fr]

                   Hello all,


   I've just encountered the following problem with TeXShop :

  1) Compilation stops with the error message "Missing $ inserted".
  2) If I insist and press "Enter" twice in the console, it eventually
compiles completely
and produces a fine output.
  3) By trial and error, I see that what causes this behaviour is a
"variations" array
(from the variations package) in the middle of my text.
  3) The line number displayed in the error message, l.259, is not very
illuminating
because the source text is as follows

\noindent \makebox[\textwidth][c]{
 \begin{variations}
   x  & \mI  &   & \alpha& & & 1 & & \beta&  & & 2 & & \pI & \\
   \filet
 f'(x) & \bg & + & \bb&  & + & \z & -& \bb & & - &\z& + & &\bd \\
 \filet
  \m{f(x)} & \bg \mI &  \c \h{\pI} & \bb& \mI & \c & \h{-1} & \d \mI & \bb
& \h{\pI}& \d &\frac{3}{2}& \c
  & \h{\pI} & \bd \\
\end{variations}
}<- Line 259 is here

 Can anyone help me on this ?

                                                   TIA,