You cannot return an array. Pass it in by reference or return a CSV and ALINES() it upon return.

local array laTables(1)

dbc2Convert = "\\tpdfiles\data\dfreeman\tip\data\rta\rta.dbc"
GetDBCTableNames(dbc2Convert. @laTables)

for i = 1 to alen(aTables)
? aTables(i)
next

function GetDbCTablesNames( myDBC, laTables )

select objectname as tablename ;
from (myDBC) ;
where objecttype = "Table" ;
into array laArray

return