As you may be aware, Adobe Flash is old technology which has been abandoned by mainstream developers. Hence why you may run into some issues when trying to use The Belle and Sebastian Flash Collection. This page should help you troubleshoot any common issues.
If you're unable to begin downloading, try right-clicking on the download link and selecting 'Open Link in New Window'. Once that window opens, refresh the page and the download should begin.
If your browser blocks the download and tells you it might be unsafe, then you can safely bypass the warning and download it anyway. Depending on which web browser you use the procedure for bypassing the download warning may look different.
On Windows, your computer will automatically assume that any Adobe Flash software is unsafe and will prevent you from opening the program. The Belle and Sebastian Flash Collection however, is completely safe to use. You can bypass this by clicking 'More info' and then the 'Run anyway' button.
Please read the whole paragraph below word for word before attempting any of the steps.
Unfortunately, on the latest Macintosh computers, Apple no longer allows you to open applications which are from independent developers such as I'm Interested In Apathy, requiring apps to be from the App Store or identified developers. Depending on how new your Mac is, you may be able to easily bypass this feature. Open the Settings app on your Macintosh and go to the Security Settings/Privacy & Securty pane. There, you should find a section that reads 'Allow applications downloaded from'. If there is an option available that says 'Anywhere' enable that option and try opening The Belle and Sebastian Flash Collection again by right-clicking/Control+clicking the application and then clicking 'Open'. The app should now run. If the 'Anywhere' option does not exist you will need to enable it by opening the Terminal and entering a command. Open the Terminal by starting Spotlight (Command+Space) and opening the Terminal. Once you are greeted with the prompt, copy and paste the command in bold font into the terminal sudo spctl --master-disable once the command is entered into the Terminal, pess enter to submit it and you will be asked for your password. Enter your password and the command will be processed. Relaunch the Settings app and the option to launch applications from Anywhere should be available.