error MC1000: Unknown build error.
The error detail indicated that the build cannot continue because some of my file or folder name is too long. I was working with TFS, and obviously, I understood that the local path to which I checked out my files is too long. I wanted to change the TFS source control local path. I fooled around a little, and found that I can do it from Files->Source Control->Workspaces.
You can select the Workspace in the Workspaces dialog and click Edit. In the resultant dialog box, select the new path for your branch, in place of the red line you see. TFS will move all your folders to the specified new location.
Gulp, Gulp :).