A collogue of mine was having issues with getting his VS.NET 2008 Solution connected to TFS or online, his solution can be found here.  However, his trick did not work for me as the registry hive mentioned did not exist.  I was unable to click the icon to put the solution back online in the Solution Explorer even after a cache reset.  I ended up having to remove my solution mapping and recreate it before I could click the button to get the solution back online.

Resetting the cache using VS Command Prompt below did not work.

tf workspaces /s:http://yourserver.com:8080 /noprompt

Removing my solution mapping from TFS, adding it back, GLV finally allowed me to click the button in Solution Explorer to get the solution back online.

Steps:

1. Open Solution Explorer
2. Right click on Folder MyProjectName select “Remove Mapping” from menu
3. Right click on Folder MyProjectName select “Add Mapping” from menu
4. You will be prompted to perform a Get, follow directions
5. Open Solution, in Solution Explorer click the Online icon at the top