1 - Turn on PHP debugging in the system admin section of your site and post back any errors you're getting. Hopefully someone can help you from that.
2 - If problem rectification is urgent, I assume you made a backup prior to installing Catzwolf's new downloads module as it is only in it's release candidate stage. Roll back to your backup and continue on using the standard MyDownloads module until the new MyDownloads module has matured a little.