Errors Exporting A View

I am trying to export a view defined as follows (to cleanse data):

Create View Cleanse_View as
SELECT Primary_Key, Name, Value,
SUBSTRING(Name, 1, len(Nam) - len(Value)) AS Test_Method
FROM My_Table


THE FOLLOWING ERROR IS GENERATED WHEN EXPORTING (USING SELECT, etc):

Server: Msg 536, Level 16, State 3, Line 1
Invalid length parameter passed to the substring function.
The statement has been terminated.

Any ideas of what's causing this because the view works fine?

Thanks
Ziggy