The ODBC functions assume that the largest piece of data you'll need to read from a single column will be no bigger than 256 characters (bytes). If you need a larger size, then you should call OdbcResultsSize to set the desired size.
/* Set the results buffer to 1000 bytes. */
OdbcResultsSize(1000)
To query the current buffer size, call OdbcResultsSize with no args:
SAY "Current size =" OdbcResultsSize()