The problem is caused by variable persistence.
The update page uses a URL Variable to filter the rsGetSelectedRoom recordset,for example:
eid=18
in the update record behavior the $row_rsGetSelectedRoom['RmConfigIdx'] is used to tell which record to update.
When the page first loads, the eid UTRL variable is present, so the recordset has a value, when the form posts, the eid URL is not included, so the recordset is empty, the iupdate does not know what record to update.
to fix this, chnage the forms action:
<form class="Basic_Default" id="UpdateRoom" name="AddRoom" method="post" action="<?php echo (htmlentities($_SERVER["PHP_SELF"], ENT_QUOTES)); ?>">
to:
<form class="Basic_Default" id="UpdateRoom" name="AddRoom" method="post" action="<?php echo(htmlentities($_SERVER["PHP_SELF"], ENT_QUOTES)."?".$_SERVER["QUERY_STRING"]); ?>">
this will pass the query string when the form is submitted.