Error using fndload for key flex fields

I am getting the following errors when attempting to use fndload to upload key flex fields:

ORA-20001: LDR.up_kff_column()(LEAF, XXINV, FFT, CODE_COMBINATION_ID) raised exception.

ORA-20303: COL:CODE_COMBINATION_ID is used by APP Id: Flex Name: Usage Code:K. You cannot use it in another flexfield.

I have been unsuccessful in searching for a similar error listed in the knowledge base or for that matter the internet itself. If anyone has come across it before or could shed some light I would greatly appreciate it, thanks.