joe fails when opening a lua source file

Binary package hint: joe

Ubuntu Hardy up to date

joe version 3.5-1.1

When i open a lua source file with joe (jmacs) such as:

>>>
-- defines factorial
function factorial (n)
   if n == 1 then
      return 1
   else
      return n * factorial(n - 1)
   end
end

print("Enter a number:")
num = io.read("*number")
print("\n")
print(factorial(num))
<<<
 I get

 /etc/joe/syntax/lua.jsf 183: Unknown class

 And i can not edit the file.