Hi Gokul,
We have released a new version of the Showcase app on Friday, however the download button may not refer to the latest version yet. Could you please go to the Releases tab, manually install the latest update that has been uploaded there and try to run it? There was an issue because of some java dependencies from the Community Commons module which was fixed before the release. If this is similar to your current problem, you can also try installing the newest version of the module from Mendix Marketplace.
Best,
Ayca