Error on opening project

We are facing issues opening existing projects. We get following two error messages one by one wheb opening any project:

1. queryBranch : Error applying query. Can not get item with id=FB26763E5354E67A795A4F9AC2E6E
2. Error 890 : Failed to get Wbs Element with id=FB26763E5354E67A795A4F9AC2E6E and levels= 1

Please help, we blocked to proceed further.