An insert statement on a MS Access database table only works once in the same script:

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  if ($conws=odbc_pconnect("DB1","Admin","")) {
    if ($result=odbc_exec($conws,"insert into MessageQueue (MsgType) values ('MESSAGEONE')) { 
      if (odbc_commit($conws)) {
          $result=odbc_exec($conws,"insert into MessageQueue (MsgType) values ('MESSAGETWO')");
          odbc_commit($conws);
      }
  }
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MessageQueue is a table with one field: MsgType without an index or constraint. 
The second insert is not done, although the 'odbc_commit's are succesfull and 'odbc_exec's do return a handle.