Maybe let it just download/install overnight, the TF2 servers have been experiencing loads of traffic since it went free to play so it's not surprised downloading it is a bit sluggish. Let it sit for a bit.
---------- Post added at 07:40 PM ---------- Previous post was at 07:06 PM ----------
Solved
Renaming ClientRegistry.blob
It's possible you may be receiving this message if Steam isn't properly configured or if configuration files are missing.
Renaming the ClientRegistry.blob will cause Steam to re-download fresh copies of required configuration files, which can solve a large number of issues.
On Windows
If the issue is isolated to a few Steam games, please exit from Steam and go to the Steamapps folder (default is CProgram Files\Steam\Steamapps) and delete any listed .ncf files for the specific games. Once complete, please restart Steam to test the issue.
On Mac
If the issue is isolated to a few Steam games, please exit from Steam and go to the ~/Users/[username]/Library/Application Support/Steam/SteamApps and delete any listed .ncf files for the specific games. Once complete, please restart Steam to test the issue.
---------- Post added at 07:43 PM ---------- Previous post was at 07:40 PM ----------