Im guessing you have signed out, then back in and the message still persists. Exit steam then go to your steam folder ( C:\Program Files\Valve\Steam\ or C:\Program Files\Steam\ ), However it is setup for you. Locate "clientregistry.blob" and delete it. Restart Steam, and see if it continues.
If it does, follow these instructions found from Steam's website.
Quote:
If deleting the clientregistry.blob file does not resolve the issue, please exit Steam and delete everything under the Steam installation directory except Steam.exe and the /SteamApps folder - this will force Steam to update when you log in
If the issue persists, please see the Verifying GCF Cache Files article for instructions to repair your game cache files
Also, this error can be caused by having certain Steam files set to Read Only. To resolve this:
Exit Steam.
Navigate to the directory where you installed Steam. (Typically C:\Program Files\ or C:\Program Files\Valve\.)
Right-click on the Steam folder.
Select Properties.
Check the Read-Only checkbox and press Apply.
Uncheck the Read-Only checkbox and press Apply.
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[Splak Server Administrator]
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