Dear 
Condition type KOFK with A/C Key "ERL" had allready been setup in VKOA before finding the above error "KI280".
Dear JP,
The "Profit Center" is not selected under "Costing 1" tab of our respective material master and it is not used for our Controlling Area.
Also, I know that the problem should be able to resolve after creating cost element for the relevant GL A/C in our current server (SAP client 138), but it is not required to create cost element for the relevant GL A/C while Invoice can be release without error in our another server (SAP client 118). This process has been using for nearly 4 years in this SAP client. Do you mean this process is inappropriate ? Anywhere else can still be suggested to check and compare between these two SAP clients ?
Many Thanks,
KH Fong