RODBC displays NA for blank values and tables containing no data. R on the other hand, will return a message. This issue is caused when data is returned from the Aster Database to R, numeric columns in an empty table are recognized as "character" data types, which is a limitation of RODBC.
The NA value reported by RODBC is the result of the Aster Database returning NULL for a query with a function against an empty table that RODBC then converts to NA.