Facing error while registering target application to load metadata into planning application.

I want to load metadata using flat file (txt) . I could successfully register the source system.

Next to add target application , clicked on add in the Target application setup option. And selected Dimensions from the dropdown , as it is a metadata load.

Clicked saved.

Next clicked on the account dimension and started to select the dimension properties as per the source file.

In the source file , there aggregation field , so selected aggregation property as well.

Next , click on save. Getting the below :

"dimension name aggregation () already exists. please enter another dimension name"

I unchecked the aggregation property and tried to save. But still showing the error.