Help - Lua Error

[DaveSCUSA]

I keep getting this error after a var has been filled:

   106890 LUA: Global: DVar = Fuel_L_Bravo OFF
   106906 LUA: C:\FSUIPC7\Test_Keys.lua:46 fn: UpdateWnd
   106937 LUA: C:\FSUIPC7\Test_Keys.lua:47 fn: UpdateWnd
   106953 LUA: C:\FSUIPC7\Test_Keys.lua:48 fn: UpdateWnd
   106968 *** LUA Error: C:\FSUIPC7\Test_Keys.lua:48: attempt to concatenate global 'Dvar' (a nil value)

Have been over examples, plug-ins. Can't seem to find where it is wrong (my eyes may be getting too old).

function UpdateWnd()
    ipc.writeUD(0x66C2, 5)  -- Set Bravo for  Message
    if val == nil then
        mess = (" T - "..Dvar)
        ipc.writeSTR(0x3380,mess)
    else
        message = (" T - "..Dvar.." Value = "..val)
        ipc.writeSTR(0x3380,mess)
        val = nil
    end
end

PS - This is a test lua to double check using the events in the aircraft

Test_Keys.log Test_Keys.lua

[John Dowson]

Dvar isn't defined anywhere, so when you declare it in a function I suspect it will be local to that function - try defining DVar at the top of your script, e.g.
    local DVar = "no value"

the variable val used in function UpdateWnd() is also never declared and will always be nil.