Many users were being greeted by a 'Working...' message when trying to download an app from the Beta Store in build 10080. Luckily, this issue has now been fixed, though your mileage may still vary.
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Microsoft has recently released Windows 10 build 10049 with Spartan for 'fast ring' Insiders, and with this new release you get the ability to test the Music and Video preview apps.
Some people are reporting that there's a problem with the beta Store app, which might refuse to open or update, preventing you from testing Office Preview apps, but we have an easy fix for that.
Just two weeks after releasing build 9926 to Windows Insiders, Microsoft has provided the first update to a universal app. Photos Preview has now been bumped to version 15.130.1615.0.