(From Microsoft Knowledge Base Article – 246509)
When a program that is deployed through Group Policy is not installed correctly on a client computer, a log file can be generated that records the steps of the Group Policy Application Deployment component leading up to the unsuccessful installation. This information, in conjunction with logging from the Windows Installer service, can be very helpful in determining the cause of the problem.
To enable verbose logging of Application Deployment operations, add the following registry value on the client computer. Delete this value after troubleshooting to avoid performance degradation:
Key: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Diagnostics
Note that you may need to create the Diagnostics key.
Value: AppMgmtDebugLevel
Type: REG_DWORD
Data: 4b
The logging file is named Appmgmt.log and is located in the %SystemRoot%\Debug\Usermode folder on the client computer.