toolchange_gcode generates error on placeholder  

toolchange_gcode generates error on placeholder

I need to enter some instructions in the Toolchange Gcode, but some of them generate an error while slicing, but the gcode file is still generated and no errors are generated to the cache-file to which the error message refers

The code which generates an error is:

;TOOLCHANGE specific GCODE
M117 Prepare cooldown extruder [current_extruder]
M117 Temperature: S[temperature_[current_extruder]]
M117 Standby temp: S[standby_temperature_delta]
M104 S[standby_temperature_delta] ;make sure the temp at least drops to the standby temp

T[next_extruder]
M117 Prepare heat up extruder [next_extruder]
M104 S[temperature_[next_extruder]] 
M109 S[first_layer_temperature_[next_extruder]]

When I remove the two bold lines no error is generated.

Are these parameters forbidden in the toolchange_gcode or is this a bug. What would be a solution to this behaviour?

BTW this code is of course, in the current form, useless, but needs to be further completed to solve the problem that the temperature of the extruders is not correctly set when printing a wipe tower