One of the team member on opening the project (SSAS) using SSDT found out that there are no more locks on the files. The TFS association with project was lost. When we navigate through source control explorer we could see the project in TFS.
The reason this time was the project had gone offline. We opened the project. Navigate to File=> Source Control and you should see the option to make project online. Go ahead and click on it.
For some other team member it automatically prompted with “Go Online” message: The solution is offline but its associated Team Foundation Server is available. Would you like to go online with this solution after it has loaded?
Click on “Yes”. Please wait and Viola ! all the TFS association will be back.
Also you can find same information about how to get back online.
The reason other time was the project had lost its bindings. To fix this issue we did TFS binding. In the open project in SSDT / Visual Studio, select the solution file and navigate to: File => Source Control => Advanced => Change Source Control.
If you see SERVER NAME and SERVER BINDING missing. That is the problem.
Just click on BIND.
Also you can find same information about how to bind the project and solution file.