SQL Server Express Mgmt Tools ONLY Installation Error on 10317cdd.msi

Installing  SQL Server Express Mgmt (Tools Only) onto a Windows 7 Pro machine which already has SQL 2008 R8 Developers Edition installed. I only need the 2012 Management Studio to work with a remote 2012 Database.
Installation stops with following error: "SQL Server Setup has encountered the following error: C:\Windows\Installer\10317cdd.msi."

Here's the last few lines with the error of the detail.txt file in the installation log folder:
ActionKey action, ActionMetadata actionMetadata, TextWriter statusStream) (01) 2013-08-02 13:05:50 Slp:    at Microsoft.SqlServer.Setup.Chainer.Workflow.ActionInvocation.InvokeAction(WorkflowObject metabase, TextWriter statusStream) (01) 2013-08-02 13:05:50 Slp:    at Microsoft.SqlServer.Setup.Chainer.Workflow.PendingActions.InvokeActions(WorkflowObject metaDb, TextWriter loggingStream) (01) 2013-08-02 13:05:50 Slp:    at Mic ...