Failed to instantiate file "default.master" from module "DefaultMasterPage"

I ran into this error while trying to create a new Site Definition in SharePoint 2010.  It turns out that the TemplateName you select in your webtemp_custom.xml file:

<Template Name="CustonSiteDefinitions" ID="10000">

Must match the folder in your SiteTemplates directory:

14/TEMPLATE/SiteTemplates/CustomSiteDefinitions

otherwise you'll get the error above.