The problem is that the current installer chooses the folder that version 5.X.X of ProTools uses to store its available plug-ins. The easy workaround for this is to reinstall Sampletank and only select the the RTAS option as being installed, then in the next step when it asks you to specify the folder that the plug-in will be isntalled in, hit the browse button and navigate to C:\programfiles\commonfiles\digidesign\dae\plugins and choose this folder as the destination.
Now in ProTools you will have Sampletank available to you.