MassUpdate Javascript Error On Custom Module

[CMTG]

Hi,

I'm running SugarCRM OS 4.5.0h on WindowsXP/IIS5.1.

I've written a custom module using the stock Opportunities module as a template. It all works great except for the mass update form at the bottom of the ListView. When I click the Update button, I get a Javascript error:

Line: 445
Char: 3
Error: 'document.defaultView' is null or not an object
Code: 0

The lines surrounding 445 from the generated web page:

[Line 443] <li  id="tab_li_Opportunities|basic_search"><a  id="tab_link_Opportunities|basic_search" href="javascript:selectTabCSS('Opportunities|basic_search');">Basic Search</a></li>	
[Line 444] <li  id="tab_li_Opportunities|advanced_search"><a  id="tab_link_Opportunities|advanced_search" href="javascript:selectTabCSS('Opportunities|advanced_search');">Advanced Search</a></li>	
[Line 445] <li class="active" id="tab_li_Opportunities|saved_views"><a class="current" id="tab_link_Opportunities|saved_views" href="javascript:selectTabCSS('Opportunities|saved_views');">Saved Search & Layout</a></li>
[Line 446] </ul>
[Line 447] <script>SUGAR.savedViews.displayColumns = "OPP_NUMBER|SUFFIX|NAME|ACCOUNT_NAME|SALES_STAGE|AMOUNT_USDOLLAR|DATE_STAGE_CLOSED|DATE_CLOSED|ASSIGNED_USER_NAME|BIZ_GROUP";SUGAR.savedViews.hideTabs = "OPPORTUNITY_TYPE|COUNTRY|MARKET|CLIENT_REF|PROBABILITY|DATE_ENTERED|CREATED_BY_NAME|MODIFIED_USER_NAME";</script><form name='search_form'><input type='hidden' name='searchFormTab' value='saved_views'/><input type='hidden' name='module' value='Opportunities'/><input type='hidden' name='action' value='index'/><input type='hidden' name='query' value='true'/><div id='Opportunitiesbasic_searchSearchForm' style='display: none'>

Mass update still works fine for all of the other stock modules.

It is very non-obvious to me how the mass update works, even after spending weeks learning how to write modules and I'm not even sure how that piece of code is even related to mass update. What have I missed?

Any help greatly appreciated.

CMTG