I have some problem with OOMMF simulation

Question

   Specify Oxs_ScriptUZeeman [subst {
      script_args total_time
      script {SmoothStep $step_height [expr {$rise_time*1e-12}]}
      multiplier [expr {0.001/$mu0}]
   }]

   proc SmoothStep { Hnom risetime t } {
      set t [expr {$t/$risetime}]
      if {$t<=0.0} {
         set g 0.0
         set gp 0.0
      } elseif {$t>=1.0} {
         set g  $Hnom
         set gp 0.0
      } else {
         global pi
         set g [expr {0.5*$Hnom*(1-cos($pi*$t))}]
         set gp [expr {0.5*$Hnom*$pi*sin($pi*$t)/$risetime}]
      }
      return [list $g 0 0 $gp 0 0]
   }

I simulated mif file that is littele bit changed from yoyo.mif file which is contained with oommf file. but it's not working now. Program said that Can't use non-numeric string as operand of '/'. I tried to solve this problem, but it does not resolved yet.