Failed to completely create the top-level Web site

I tried creating a custom site template however the template name and the folder name within 14/SiteTemplates didn’t match and I received the following error:

Event log message was: ‘Failed to completely create the top-level Web site.’. Exception was: ‘Microsoft.SharePoint.SPException: Failed to instantiate file “default.master” from module “DefaultMasterPage”: Source path “default.master” not found

I looked around for the same error and found many reasons but not many people with fat fingers like I have. Silly typos!

Anyway, what is happening? When a site definition isn’t found SharePoint seems to assume some defaults and picks up the default onet.xml? resulting in the above error. Not very useful, but at least consistent.