Hi Merve,
When you are calling this function module are you calling it from webui, from your order?
If so, that's strange, it worked from me previously. Which version are you working with?
Also, in debug, you can see all the entities available in variable lr_gdc (lr_gdc > GT_ENTITY). You can try that or try another entities names available in if_iccmp_global_data_cont_con interface. Maybe you can investigate a little there.
Kind regards,
Bruno