Populate Indexed Table in Oracle Using Informatica

I'm new to both Oracle and Informatica. Currently working on a small task where I need to select all records from the source table, filter the results to get only records where field1='Y' and finally insert new rows into the target table that contains only src.field2 and src.field3 values.

These 2 fields are used for the PK and for the Index of the target table.

So i get an error in Informatica:

"ORA-26002: Table has index defined upon it"

I rather not dropping the index? is there a work around?

I've tried alter index to "unusable" but I got the same error.

Please advice.

Thanks.