double sqlexec();

Hellow, i have one question. When i call system functions sqlexec(dbbproc) should i clear some buffers after that? I have two peace of cod. At the first one
 
 sqlexec(db_);
  dbbind(db_, 1, NTBSTRINGBIND , 0, (BYTE*)var);
  while (dbnextrow(db_) != NO_MORE_ROWS)
  {
                        printf("%s\n", var);
  };  
  
  sqlcmd(db_,somebuff);
  sqlexec(db_);

everything works correctly. But in the second one

sqlexec(db_);//
sqlcmd(db_,otherbuff);
sqlexec(db_)               

i received a mistake in sqlexec(db_) functions "FreeTDS: db-lib: exiting because client error handler returned 20002 for msgno 20019"