Srini is correct, but there are ways you can do what you need without OBIEE getting unhappy. One quick solution would be to create a logical table from a formula based on the table you need to import. Then join the two tables together in the logical column. Drag both to presentation layer.
This will allow OBIEE to validate and you will be able to see the results in Analytics if you create a quick analysis.
You can make alias for that table and made a join and drag both table to BMM layer and the main table to presentation Layer.