Windows Store apps and error 0x8007274C

Wednesday, August 27, 2014

We are receiving reports from multiple customers that they are unable to connect a Windows Store app to XAML Spy. Connection error 0x8007274C is shown, which indicates that the store app is unable to connect to the XAML Spy service hosted on the local machine.

In the past this error occurred when the project setting ‘allow local network loopback’ was unchecked. Checking the option, solved the issue. Now however, the error seems to occur even when the project setting is correctly set.

We do not know yet why this error occurs. We are currently investigating the cause of this issue, and will update this page when news is available.

Silverlight, Windows Phone and WPF apps seems to be unaffected.

Update September 1

It seems that the issue is related to having many Windows 8.1 AppContainers that are exempt from the local network traffic restriction. Resetting all loopback exemptions seems to solve the connection issue for XAML Spy.

Below the steps to manually reset all loopback exemptions. The steps require Fiddler, a free web debugging proxy from Telerik. Make sure you have installed this tool.

  • Launch Fiddler
  • Launch the EnableLoopback tool by clicking the Win8 Config button in the toolbar. The tool requires elevated permissions, you’ll need to accept it in the User Account Control dialog that is shown. The EnableLoopback tool lists all AppContainers and whether they are exempt from the local network restriction.
  • Reset all loopback exemptions by clicking the Exempt None button followed by Save Changes. All Windows 8 apps are now blocked from connecting to the local machine.

Resetting loopback exemptions will disallow any app from connecting to the local machine. Visual Studio automatically re-enables the exemption when an app is launched from Visual Studio. If your app does require the loopback exemption, even without debugging, you’ll need to exempt it manually with Fiddler.

Why the behavior occurs is still unknown, our investigation continues. We are looking into the behavior of the XAML designer in Visual Studio, it might be related. It does create many AppContainers named that eventually cause XAML Spy to stop connecting.