When attempting to launch the designer, the downloading dialog box will appear. The progress bar will move slightly then look as if it freezes. There will not be any error messages or logs for this event. AVG antivirus software has been known to cause this condition.
Disable your antivirus software.
Update: AVG antivirus can be enabled if you disable the Surf Shield within AVG.
1) Open AVG
2) Click the LinkScanner component
3) Clear the Enable Surf-Shield check box
4) Click Save Changes
Solution can be found on the AVG website here
4368 Disabling AVG Surf-Shield