Accounts requires assignment to CO object for cost element category 11

During GL parking, error pops up. This revenue account is assigned to a Cost center and profitability segment and the cost element category is 11 (Revenues). When the cost element category is changed to 1 (Primary cost) with the same assignment as above, the document parks. It throws error only when cost element category is 11. I have checked the FSG settings and CO object or Profitability segment are optional fields. Please advise what could be causing this error.

Thanks

Kim