I opened a solution in offline mode. But now I am trying to go online and connect to tfs but I cannot seem to see the \"Go Online\" Button under File-> Source Control.
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I faced the same problem when i worked on my solution when i was disconnected from tfs.
I unloaded and loaded the project i worked offline and suddenly go online option showed.
I think doing that checks out the project so that unknown bindings are removed.
You may have to delete the bindings of existing projects that failed to bind correctly.
Then close the binding dialog.
Now you can add each of the disconnected projects from your solution explorer.
This ranges somewhere between buggy and pathetic, but if you click around on sufficiently many seemingly unrelated menus, context menus, and dialogs, you may guess how to repair the TFS connection like this
I found out that the "File > Source Control > Go Online" menu item doesn't appear when the "Source Control Explorer" window is active.
So you will have to open a different window and\or file.
In my case, when I opened a .cs file within a project of the open solution, the "Go Online" menu item was available once again.
This is not ideal, but another option is to close Visual Studio and open it again.
In my case whenever I get disconnected (we use TFS online) then after a drop in connectivity my VS thinks it is still offline, I cant convince it otherwise so when I restart VS it then forces it to check connectivity and then my solution is automatically back "online".
Try File > Source Control > Change Source Control, and then bind your solutions/projects.