"This game is currently unavailable. Please try again at another time."

Just recently I’ve been getting this error when trying to start up Garry’s Mod. I get the same problem with TF2. Is anyone else getting this problem? Does anyone know the cause of this problem, or how I can fix it?

Here are my computer’s specs, if it matters:

Operating System: Windows 7 Home Premium 64-bit (6.1, Build 7601) Service Pack 1 (7601.win7sp1_gdr.110622-1506)
Language: English (Regional Setting: English)
System Manufacturer: System manufacturer
System Model: System Product Name
BIOS: Phoenix - AwardBIOS v6.00PG
Processor: AMD Phenom™ 9150e Quad-Core Processor (4 CPUs), ~1.8GHz
Memory: 8192MB RAM
Available OS Memory: 8190MB RAM
Page File: 2460MB used, 13918MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 11
DX Setup Parameters: Not found
User DPI Setting: Using System DPI
System DPI Setting: 96 DPI (100 percent)
DWM DPI Scaling: Disabled
DxDiag Version: 6.01.7601.17514 32bit Unicode