One of my clients had a problem after they re-inherited a custom master page through an entire MOSS website. After they did this, the recurring meeting workspace hyperlinks under “Select a date from the list below” throws a "g_instanceID is not defined" JavaScript error.

This problem occurred because when a Meeting Workspace is created it uses it’s own master page called mwsdefault.master which is found in the TEMPLATE\GLOBAL directory in the 12 hive (c:\program Files\Common Files\Microsoft Shared\web server extensions\12\Template\Global). This master page has placeholders and code that are typically not found in other master pages and the g_instanceId global JavaScript variable is declared in a script registered runtime by the Microsoft.SharePoint.Meetings.PropertyBag web control.

If you want to use your own custom master page you can fix this by merging the missing code located from the mwsdefault.master and put it into your custom master page. The Best Practice is to create a feature to automatically set Meeting Workspaces to your modified custom master page file.

To fix this problem in your custom master page you need to:

1. Copy the register Microsoft.SharePoint.Meetings tag prefix from the mwsdefault.master and add it to your custom master page.

<%@ Register Tagprefix="Meetings" Namespace="Microsoft.SharePoint.Meetings" Assembly="Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>

2. Then copy the Meetings:PropertyBag control into your custom master page.

<Meetings:PropertyBag runat="server"/>

3. Save master page, check in (if necessary), and publish the major version or deploy it in your feature.