From loading a save, unable to start playing again:

The mod RPG System (1.3.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event RPGsystem::on_configuration_changed
real number expected got nil.
stack traceback:
[C]: in function 'newindex'
__RPGsystem/control.lua:806: in function 'UpdatePanel'
RPGsystem/control.lua:383: in function 'InitPlayerGui'
RPGsystem/control.lua:213: in function 'CheckPlayers'
RPGsystem/control.lua:325: in function 'XPModSetup'
RPGsystem/control.lua:1135: in function <RPGsystem/control.lua:1134>