Today when I came to the office and looked at our Project Dashboard, I felt surprised why the section of work items showed the error.
This query is from the folder of Team Queries in TFS and it is also a Server Query from the viewpoint of Project Dashboard. After looking into this issue, Dashboard folder was gone in TFS. I reported to my QA manager and later I joined the Scrum.
After he looked into it, he found out the issue. Thanks God. For some reason, someone moved it to another sub-folder and it was not deleted.
After moving it back to the original location, the Project Dashboard is showing up as expected.