I've been getting regular errors from Visual Studio due to the VS Extensions experiencing and exception. It's not specific to the "UI for Silverlight" extensions and happens with the others too.
Here's the exception information from the ActivityLog.xml.
Please log the bug to be fixed.
<entry>
<record>912</record>
<time>2014/12/11 02:47:06.576</time>
<type>Warning</type>
<source>Telerik.Windows.Silverlight.VSPackage.VsPackage</source>
<description>Failed to query command status: System.Runtime.InteropServices.COMException (0x80004005): Unspecified error (Exception from HRESULT: 0x80004005 (E_FAIL))
 at EnvDTE._DTE.get_ActiveSolutionProjects()
 at Telerik.VSX.Internal.ProjectManagement.ProjectRetriever.GetFirstActiveSolutionProjectOrNull(DTE dte)
 at Telerik.VSX.Internal.ProjectManagement.ProjectRetriever.GetFirstSelectedProject(DTE dte)
 at Telerik.VSX.Internal.ProjectManagement.ProjectWrapFactoryBase`1.GetForFirstSelectedProject(DTE dte)
 at Telerik.Windows.Silverlight.VSPackage.CommandStateController.GetState(OleMenuCommand command, DTE dte)
 at Telerik.VSX.CommandStateResolving.CommandStateControllerBase.GetAsyncState(OleMenuCommand menuCommand, DTE dte)
 at Telerik.VSX.VSPackage.PackageBase.MenuCommand_BeforeQueryStatus(Object sender, EventArgs e)</description>
</entry>
Here's the exception information from the ActivityLog.xml.
Please log the bug to be fixed.
<entry>
<record>912</record>
<time>2014/12/11 02:47:06.576</time>
<type>Warning</type>
<source>Telerik.Windows.Silverlight.VSPackage.VsPackage</source>
<description>Failed to query command status: System.Runtime.InteropServices.COMException (0x80004005): Unspecified error (Exception from HRESULT: 0x80004005 (E_FAIL))
 at EnvDTE._DTE.get_ActiveSolutionProjects()
 at Telerik.VSX.Internal.ProjectManagement.ProjectRetriever.GetFirstActiveSolutionProjectOrNull(DTE dte)
 at Telerik.VSX.Internal.ProjectManagement.ProjectRetriever.GetFirstSelectedProject(DTE dte)
 at Telerik.VSX.Internal.ProjectManagement.ProjectWrapFactoryBase`1.GetForFirstSelectedProject(DTE dte)
 at Telerik.Windows.Silverlight.VSPackage.CommandStateController.GetState(OleMenuCommand command, DTE dte)
 at Telerik.VSX.CommandStateResolving.CommandStateControllerBase.GetAsyncState(OleMenuCommand menuCommand, DTE dte)
 at Telerik.VSX.VSPackage.PackageBase.MenuCommand_BeforeQueryStatus(Object sender, EventArgs e)</description>
</entry>