I have created a simple Segment rule to pull all the customers.  When I save and run the segment I get the following error message:

I am seeing the following error in the log file as well:

Error while performing insert into tmp table with SQL: INSERT INTO segallC0(pySubjectID, pyGroupID, CriteriaID) SELECT customerid AS pySubjectID, customerid AS pyGroupID, 0 AS CriteriaID FROM (SELECT PC2.customerid, PC2.customerid FROM externalmktdata.Engagecustomer PC2 WHERE (PC2.firstname IS  NOT NULL)) src 
org.postgresql.util.PSQLException: ERROR: column reference "customerid" is ambiguous 

Any advice?