Error message during a Design Transfer import:
"An intermal exception has occurred while committing attributeType <attribute title>:
Mandatory attribute _<attribute name> does not specify a default value. When adding a new mandatory attribute to an existing class type you must specify a default value."
This is a known issue that stops a design transfer working if you are importing an object that contains mandatory attributes, and they not also the IsName attribute for that object. This is logged as Problem 3981 but at present (v7.2.6) there is no fix for this.
The workaround is to make these attributes non-mandatory. Unfortuantely this is something that cannot be changed after the attribute has been created so to get around this you must remove and re-create the attribute.
As you cannot make the attribute mandatory at object level when using Design Transfer we recommend you configure the fields on your window design to be mandatory instead to achieve the same effect.