An error occurs when a user is not able to create any new dynamic dashboard: You reached the limit for Dashboards run as the logged-in user.
This organization is an Unlimited Edition organization. It can have a maximum of 10 Dynamic Dashboards. As of now, there are 10 Dynamic Dashboards created and as such, the user is not able to save another one.
Consider increasing the number of Dynamic Dashboards. Note: There is an additional cost to do so.
Or, clear the Recycle bin for the deleted Dashboards. After this is done, the user should be able to create a new Dynamic Dashboard.