App fails to start up. The main windows is displayed, but then am prompted with the crash dialog 1-2s later. This v1.7 release had been working fine, but after the v1.8 release on 2/23, the app prompted me to upgrade. I declined. Subsequent start-ups of the app crashed.

sourcetree.log:
ERROR [2016-02-25 10:09:13,758] [1] [SourceTree.AppRoot] [HandleCrash] - Fatal error
System.ComponentModel.Win32Exception (0x80004005): The system cannot find the file specified
at System.Diagnostics.Process.StartWithShellExecuteEx(ProcessStartInfo startInfo)
at System.Diagnostics.Process.Start(ProcessStartInfo startInfo)
at SourceTree.AppRoot.LaunchPageant(Boolean promptForKeyIfBlank, String keyfile) in C:\projects\bitbucket.org\atlassian\sourcetreewin-prod\AppRoot.cs:line 2188
at SourceTree.AppRoot.DoStartupTasksAfterFirstWindowDisplayed() in C:\projects\bitbucket.org\atlassian\sourcetreewin-prod\AppRoot.cs:line 1367
at SourceTree.MainWindow.OnContentRendered(EventArgs e) in C:\projects\bitbucket.org\atlassian\sourcetreewin-prod\MainWindow.xaml.cs:line 53
at System.Windows.Window.<PostContentRendered>b__2(Object unused)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
ERROR [2016-02-25 10:11:10,609] [1] [SourceTree.AppRoot] [HandleCrash] - Fatal error
System.ComponentModel.Win32Exception (0x80004005): The system cannot find the file specified
at System.Diagnostics.Process.StartWithShellExecuteEx(ProcessStartInfo startInfo)
at System.Diagnostics.Process.Start(ProcessStartInfo startInfo)
at SourceTree.AppRoot.LaunchPageant(Boolean promptForKeyIfBlank, String keyfile) in C:\projects\bitbucket.org\atlassian\sourcetreewin-prod\AppRoot.cs:line 2188
at SourceTree.AppRoot.DoStartupTasksAfterFirstWindowDisplayed() in C:\projects\bitbucket.org\atlassian\sourcetreewin-prod\AppRoot.cs:line 1367
at SourceTree.MainWindow.OnContentRendered(EventArgs e) in C:\projects\bitbucket.org\atlassian\sourcetreewin-prod\MainWindow.xaml.cs:line 53
at System.Windows.Window.<PostContentRendered>b__2(Object unused)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)

Thank you.