"The template you have chosen is invalid or cannot be found"
I
learned that you need to be very careful to avoid conflicts with IDs
already used in Windows SharePoint Services. It is suggested to use
UNIQUE values greater than 10,000 for the ID attribute. Also the
template ID must be unique from the ID's used in all the webtemp.xml
files, i.e. don't have two that specify ID="10001".