What does error "the Classic Environment is no longer supported" mean? I created a .app file that is 303KB on disk. When I right click it and press Compress... I end up getting a 8.4MB .zip archive. 

I tried sending the .app via email to myself and compressing it on Windows, and was able to get a .rar file of 177 bytes. However, attempting to open the .app on OSX results in the message:


  You cannot open the application...the Classic Environment is no longer supported`


What does this error mean?
The Classic Environment is Apple's software that supports running Mac OS 9 apps on Mac OS X. ("Mac OS Classic" refers to Mac OS versions before Mac OS X.) Both Mac OS 9 and Classic are really old: Mac OS 9 was discontinued in 2001, and the last version of OS X to support Classic is 10.4 (Tiger), which was released in 2005.

What's the difference between Classic and OS X apps? Their code is completely different, as different as the difference between Windows and Mac apps. This is because Classic and OS X are very different architecturally.

Why did Mac OS X think your app was a Classic app? Most likely:


On UNIX systems, which includes Linux and Mac OS, launchable program files (executables) must have a executable property set to true.
Windows and Mac OS Classic are not UNIX and their filesystems don't have the concept of a executable property.
Most Mac OS apps are folders that appear as files in Mac OS. You know this if you've looked at the app in Windows. The executable part of the app is one of the files in TheApp.app/Contents/MacOS.
When you moved the file to Windows, the executable file property was lost, so when you moved it back to your Mac, the executable property became set to false.*
When you opened the app, Mac OS tried to launch the app, noticed that the app wasn't marked as executable, and figured it must be a Classic app.


* Usually files that come from non-UNIX systems will have the executable property set to true by default, e.g., if you move files using a flash drive or if you use zip instead of rar. The program you use to unrar files on your Mac would be the one to blame.

Why was your rar 177 bytes? Perhaps because there were entire files that were unsupported and so didn't get rar'd.