basic pay infotype

Hi dears,

I have a problem with Planned Compensation (IT1005) and Basic Pay (IT 0008). So, I want to give to my employee 2 basic pay with different wage types.

T539A table and LGMST feature are configured, When I create IT0008 I see 2 lines. But, when I save my IT record the system gives me a pop-up message such: "Amount is Overwritten From Position" - Message no. 00398.

After clicking enter button it changes the second wagetype to the first. I dont know why.

PS: I created for Planned compensation just one of them. Might it be a reason?

thanks and regards,

Samir