While compiling this random numeric question:

\usepackage{fp}
...
\element{random numeric question}{
\FPeval\VQfor{trunc(30+random*10,0)}
\FPeval\VQsol{clip(((\VQfor)+5)/4)}
\begin{question}{test question}
Calculate (\VQfor{}+5)/4
\AMCnumericChoices{\VQsol}{exact = 0, decimals = 1, digits = 3, sign = false, scoreexact = 1, approx=2, scoreapprox=1}
\end{question}}

I get this error message: 3/30 good answers not coherent for a simple question [0:test question]

What's wrong with it?