Same problem for me. I bought and installed W&G game in April 2013, it worked fine (except the Toast bug in Episode 1, see separate thread). Now W&G won't launch any episode, always throws a "c0000005 access denied" critical error in my Windows 8 x64. Only system changes since April are normal Windows Updates, NVidia graphics driver updates, Windows Defender program & virus definition updates. DXDiag reports NO problems with DirectX components. Here is one (of many) UAC crash summaries:
Source
WallaceGromit101.exe
Summary
Stopped working
Date
7/18/2013 2:14 PM
Status
Report sent
Description
Faulting Application Path: D:\ProgramsZ77-D\Wallace&Gromit\Wallace and Gromits Grand Adventures\Episode 101 - Fright of the Bumblebees\WallaceGromit101.exe
Problem signature
Problem Event Name: APPCRASH
Application Name: WallaceGromit101.exe
Application Version: 2009.3.19.22137
Application Timestamp: 49c2cc74
Fault Module Name: DINPUT8.dll
Fault Module Version: 6.2.9200.16384
Fault Module Timestamp: 5010a805
Exception Code: c0000005
Exception Offset: 0000ff0e
OS Version: 6.2.9200.2.0.0.256.103
Locale ID: 1033
Additional Information 1: 5861
Additional Information 2: 5861822e1919d7c014bbb064c64908b2
Additional Information 3: f3d5
Additional Information 4: f3d5be0cad2787556264647dc02181c3
Extra information about the problem
Bucket ID: a4301acd2dd3c93c4714ce42c562c0f0 (-1177511558)
I've sent an inquiry to GOG Tech Support today, hopefully they'll advise for a solution.