You may receive an "Access Denied" error message in any of the following Microsoft programs:
Microsoft Security Essentials
Microsoft Forefront Endpoint Protection
When the issue problem occurs, the Microsoft program does not start.
This issue may occur if a version of Citrix Personal vDisk earlier than 5.6.5 is also installed on the computer.
The issue occurs because of a conflict between the filter driver in the earlier versions of Citrix Personal vDisk IVM and the Microsoft MpFilter filter driver. The conflict prevents the Microsoft Antimalware Service from starting.
To resolve this issue, install the latest version of Citrix Personal vDisk. The issue is resolved in Citrix Personal vDisk 5.6.5. For more information, visit the following webpage:
The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.