Check in the settings that "Show Beta Games" or something is ticked.
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Click the blue menu button (upper left of Impulse), and make sure the 'Show pre-release versions' option is checked. If it is, and it still doesn't show, try closing Impulse and running the following file:
http://sd.stardock.com/curthendzell/fix_registrations.reg
In IE, just follow the link, in Firefox, right click, and select 'Save Link As'. Save the file and double click it to apply it. Then relaunch Impulse. You will need to re-login with your username/e-mail (either will work) and password.
If all else fails, use the bat signal: support@stardock.com
