Wolfram Programming Cloud error Set::write: Tag Times in á l$$ $CellContext`materi is Protected

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Why I get the error below with this code:

CloudDeploy[
 DynamicModule[{fimo = 0, háček = 0, kalota = 0, karabina = 0, 
   lak = False, lanko = False, očko = 0, rokajl = 0, šlupna = 0, 
   špuntík = 0, materiál = 0, práce = 0, cena = 0}, 
  Deploy[Style[
    Panel[Grid[
      Transpose[{{Style["Polymerové hmoty", Italic], "FIMO Soft", "", 
         Style["Komponenty", Italic], "Háček", "Kalota", "Karabina", 
         "Lak", "Lanko", "Očko", "Rokajl", "Šlupna", "Špuntík", "", 
         Style["Práce", Italic], "Práce", "", 
         Style["Cena za materiál", Bold, Larger], 
         Style["Cena za výrobek", Red, Bold, Larger]}, {"", 
         InputField[Dynamic[fimo], Number], "", "", 
         InputField[Dynamic[háček], Number], 
         InputField[Dynamic[kalota], Number], 
         InputField[Dynamic[karabina], Number], 
         Checkbox[Dynamic[lak]], Checkbox[Dynamic[lanko]], 
         InputField[Dynamic[očko], Number], 
         InputField[Dynamic[rokajl], Number], 
         InputField[Dynamic[šlupna], Number], 
         InputField[Dynamic[špuntík], Number], "", "", 
         InputField[Dynamic[práce], Number], "", 
         InputField[
          Dynamic[materiál = (50 fimo)/56 + 0.5 háček + 0.5 kalota + 
             10 karabina + 0.5 očko + 0.5 rokajl + 4 šlupna + 
             0.5 špuntík; 
           If[lak, materiál += (100 fimo)/(1/35 (10 56) 35), 
            materiál]; If[lanko, materiál++, materiál]; 
           materiál = Ceiling[materiál]], Enabled -> False], 
         InputField[Dynamic[materiál + práce], 
          Enabled -> False]}, {"", "g", "", "", "ks", "ks", "ks", "", 
         "", "ks", "ks", "ks", "ks", "", "", ",- Kč", "", ",- Kč", 
         ",- Kč"}}], Alignment -> Left]], 
    DefaultOptions -> {InputField -> {ContinuousAction -> True, 
        FieldSize -> {{5, 30}, {1, \[Infinity]}}}}]]], 
 Permissions -> "Public"]

Error:

Set::write: Tag Times in á l$$ $CellContext`materi is Protected.

I obtain this error only on deployed page. When I try to run the code inside the CloudDeploy function in Mathematica, there are no problems.

Thanks,

Zdenek

Wolfram Programming Cloud error Set::write: Tag Times in á l$$ $CellContext`materi is Protected