Start by reading this. Otherwise, none of us will have a clue as to your setup or what the problem may be.

https://makemusic.zendesk.com/hc/en-us/community/posts/212952168-General-Discussion-House-Rules 

To be more concise then, I keep getting an "The Installation failed" and have plenty of space when attempting to install the GPO 4.0.2 version on a MacBook Pro, OSX 11.6.2, 16GB RAM.
GPO 5 installed without incident however.

Crash log as follows:

Jan 4 14:40:59 Ronn-MacBookPro package_script_service[872]: PackageKit: *** launch path not accessible
Jan 4 14:40:59 Ronn-MacBookPro package_script_service[872]: PackageKit: Failed task attributes: {
NSFileCreationDate = "2008-06-17 03:54:06 +0000";
NSFileExtendedAttributes = {
"com.apple.quarantine" = {length = 57, bytes = 0x30303833 3b363164 33643936 643b5361 ... 36373633 36354241 };
};
NSFileExtensionHidden = 0;
NSFileGroupOwnerAccountID = 20;
NSFileGroupOwnerAccountName = staff;
NSFileHFSCreatorCode = 0;
NSFileHFSTypeCode = 0;
NSFileModificationDate = "2008-06-17 03:54:06 +0000";
NSFileOwnerAccountID = 501;
NSFileOwnerAccountName = eeg2514;
NSFilePosixPermissions = 436;
NSFileProtectionKey = NSFileProtectionCompleteUntilFirstUserAuthentication;
NSFileReferenceCount = 1;
NSFileSize = 706;
NSFileSystemFileNumber = 8273249;
NSFileSystemNumber = 16777220;
NSFileType = NSFileTypeRegular;
}
Jan 4 14:41:00 Ronn-MacBookPro installd[827]: PackageKit: Install Failed: Error Domain=PKInstallErrorDomain Code=112 "An error occurred while running scripts from the package “AriaMain.pkg”." UserInfo={NSFilePath=./postflight, NSURL=file:///Users/eeg2514/Documents/Samples/Garritan_Personal_Orchestra_4.02_MAC/MAC_Garritan_Personal_Orchestra_4.02.mpkg/Contents/Packages/AriaMain.pkg, PKInstallPackageIdentifier=com.garritan.gapmain.ariamain.pkg, NSLocalizedDescription=An error occurred while running scripts from the package “AriaMain.pkg”.} {
NSFilePath = "./postflight";
NSLocalizedDescription = "An error occurred while running scripts from the package \U201cAriaMain.pkg\U201d.";
NSURL = "file:///Users/eeg2514/Documents/Samples/Garritan_Personal_Orchestra_4.02_MAC/MAC_Garritan_Personal_Orchestra_4.02.mpkg/Contents/Packages/AriaMain.pkg";
PKInstallPackageIdentifier = "com.garritan.gapmain.ariamain.pkg";
}
Jan 4 14:41:00 Ronn-MacBookPro Installer[72618]: Install failed: The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.
Jan 4 14:41:00 Ronn-MacBookPro Installer[72618]: Displaying 'Install Failed' UI.
Jan 4 14:41:00 Ronn-MacBookPro Installer[72618]: 'Install Failed' UI displayed message:'The Installer encountered an error that caused the installation to fail. Contact the software manufacturer for assistance.'.

I could have tried to unpack the installer, however I'm not sure as to the destination of each component.

Thoughts?

Doesn't GPO5 include everything in GPO4?

GPO4 hasn't been updated for many years, and the installer scripts likely just don't run on a modern OS.

Do you not have a backup from a previous install?

The GPO4 installer is 32 bit. No way it will run over Big Sur.

I can understand wanting it installed, though. If you have older projects that access GPO4, no need to update them to GPO5.

Do you not have a backup from a previous install?

Exactly. If you can find that and the correct location plus any components needed for License Activtion,, you should be able to copy them over. I don’t know if the current Aria Player accepts the old GPO4 authorization token, however. Frankly, we probably won’t know till you tell us.

I see GPO4 in my list of instruments available through Aria. That installation is on its 3rd Mac, however, having been transferred via Migration Assistant onto the next Mac.