Script task debug does not work when VS2012 is installed before SSDT. I was able to repro the situation on 6 different machines.
User is a local admin, local activation of COM+ and Local Debug is enabled by default but eventlog reports problems:
The application-specific permission settings do not grant Local Activation permission for the COM Server application with CLSID
to the user %s SID (S-1-5-21-....) from address LocalHost (Using LRPC). This security permission can be modified using the Component Services administrative tool.
Permission granted explicitly but the problem still persists.