It has been reported that shortcuts to "Second Life Preview" on testers' desktops that were created prior to the launch of 1.7.0 no longer work.
This is correct. The grid that hosts the 1.7.0 preview is different than the one that hosted the 1.6 preview versions. For that reason, please update your shortcuts to point to the new installation rather than any previous ones you may have had as they will no longer work correctly.