for some reason, in ms access and mdac_typ.exe 2.6 on winnt or win2k, if you try to exec query that has operation on more than 1 text field, it returns huge field size which prevents the script from executing.
ex.

$q="select firstName + ' ' + LastName from Students";
odbc_exec($c,$q);

// if you trace the odbc function calles:
call SQLColAttributes with <SQL_COLUMN_DISPLAY_SIZE>
returns
SQLColAttributes  with return code 0 (SQL_SUCCESS)
         SQLLEN *            0x0012F568 (2147483598)

so php_odbc.c in php4dll will assume that this field requires (2GB ) memory hence exits with error.
It seems like it is an odbc bug but php engine should be aware and not exceed max size limit(say 65k or be defined in the ini/conf file) for a field.