main_program: Fatal Error: Key fields must be top-level:

[pongal]

Hi,
I am using joiner stage to join 3 inputs.
1) oracle database table contains (locationtype and costcenter)
2) sequentail file contains (locationtype)
3) another sequential file contains (costcenter)

i need to map locationtype,costcenter fields with the above inputs and transform the data to destination sequential file

i have given keys fields in input link as DSLink5.locationtype and DSLink5.costcenter.
but when i try to run the job , it is gettting error "main_program: Fatal Error: Key fields must be top-level: DSLink5.LOCATIONTYPE".
i have given join type as "inner".
once again i have checked all the above input link key fields are at top only.

what would be the problem....