Name already taken, please set a new name

I am trying to create a doc type with name “Activity”. When I submit form, I get the message as “Name already taken, please set a new name”.

I do not have any other doc type with name “Activity”. What I have is shown below:

In database also, there is no table with name “activity”

Why I am unable to create doc type with name “Activity”? Is it some kind of reserved key word in Frappe?

Anyone pointer on this by anyone !

Frappe has a “Activity” page. Most probably that is the case. http://SITE/app/activity