I had the same issue. I tried to repair Visual Studio 2013, update 4, SSDT, the DAC tools, etc., but it didn't work any better.

However I noticed the Microsoft.Data.Tools.Schema.SqlTasks.targets file present in C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v12.0\SSDT was dated from 2013 (In fact it corresponded to the old SSDT). So what I did is just copy the new one (which I suprisingly found in C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v11.0\SSDT ...) over to this v12.0\SSDT folder, restarted Visual Studio 2013 and now it works. For information, that new SSDT targets file is dated from 2014/10/26 and its size is 75437 bytes.