Error/Warning: The Document Type "" will not be added because it uses a file extension that is already associated with a prior Document Type

Each time i click on my Dreamweaver CC it show a prompt screen with some warning like this,
"The Document Type "" will not be added because it uses a file extension that is already associated with a prior Document Type"
But i'm not sure why this warning or error message is showing each time at the very beginning i start my Dreamweaver CC.

Adobe Dreamweaver CC (Creative Cloud)

Version: 13.0 Build 6390

Regards

Saikot

oDesign IT Solution