One or more possible reasons as below:
1)Have you exit the payroll area after running payroll and before posting?
2)Have you done live posting?
3)Check the pay period of posting is same as what you see in pay results.
4)Check if you are trying to post an incorrect document.
5)CC assignment exists in the RT for a w/t but C0 table (in pay results) does not have a row for the Costing pointer (C0ZNR) shown in the RT w/t entry.