The Block files if scanning time exceeds (seconds) check box does not work correctly on a computer that has Microsoft Forefront Threat Management Gateway (TMG) 2010 Service Pack 1 (SP1) installed.
To resolve this issue, install the software update that is described in the following Microsoft Knowledge Base (KB) article:
2288910 Software Update 1 for Microsoft Forefront Threat Management Gateway (TMG) 2010 Service Pack 1
To work around this issue, locate and set the value in the check box to a large value manually. To do this, follow these steps:
Open the Microsoft Forefront Threat Management console.
Locate the Web Access Policy node on the navigation pane of the console, and then click the Tasks tab in the Task pane.
Click Configure Malware Inspection on the Tasks tab, and then the Malware Inspection dialog box appears.
Click the Inspection Settings tab, and then change the value of the Block files if scanning time exceeds (seconds) check box to 9999.
Click OK to apply the changes.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:
824684 Description of the standard terminology that is used to describe Microsoft software updates