In SharePoint the unattended Service Account Application ID setting will stores the application identifier in registered Secured Stored Service. Application ID will use the unattended service account credentials. If unattended service Account is single, Visio graphics service impersonates, when it connects to the data sources out of SharePoint like SQL server..etc. This account required to connect the external sources.
We can fix this issue by specifying the valid application ID value. To do that,
Navigate to SharePoint Central Administration, Application Management section and click on Manage service applications link.
Select Secure Store Service application in the list of service applications.
We have to record the application ID from the Target Application ID column.
Select Visio Graphics service application page in the list of service applications.
Click on Global Settings, in Manage Visio Graphics Services page.
we have to enter the application ID, recorded from secure store service, and enter it in Unattended Service Account text box in Visio Graphics Service Settings page, external data section, and Click on OK button.