I have limited bandwidth, so I would rather not have to re-download my games to transfer them between computers if I do not have to. While trying to copy the install files to a USB stick today, I got this message:

"Are you sure that you want to copy this file without its properties?
The file ... has properties that can't be copied to the new location."

This same message appears for several games, including Beyond Good & Evil, Prince of Persia and Legend of Grimrock II.

It DID NOT happen, however, with The Witcher 2, which I was able to transfer with no issues and works perfectly on the other machine. Is there some sort of copy protection on licensed games? Is that why it works for Witcher, but not the other titles? Were the install files somehow corrupted, and if so, how do I verify/repair them?

There is no copy protection on any of the games here. Normally you should be able to copy all games without any problem.
Sorry, can't be of much help, but it must be either some problem with your computer, usb stick or the files itself. But it is not copy protection.

That's not GOG copy protection.

Your USB stick is probably formatted as old FAT 32. Almost all Windows now use newer systems like NTFS.

EDIT:
To solve this, re-format your USB stick as NTFS.

Note:
Formatting your USB stick will erase all data on it! Back up those first!

Also, if you use NTFS, you won't be able to use the stick on old PCs using pre-Windows XP operating systems.

The properties might be related to the user account used on your local system which would then be probably NTFS and whatnot...

Try changing file permissions on the GoG folder to let everyone have access and everyone to read/write/execute in the gog downloads...

The second thought coming to mind is if any program is open that's accessing the file (Downloader) Windows loves to lock files so you can't delete or copy them. So...

Alternatively you might check the filesystem on the USB external and if it's NTFS or something then the local directory may not allow you to copy the file(s). If the USB is Fat32 there's no problem.

Google search result one: http://answers.microsoft.com/en-us/windows/forum/windows_7-files/are-you-sure-you-want-to-copy-this-file-without/fa810b7e-f228-4661-9789-2090175dd7de

Personally I use Teracopy and have had no issues copying 2-3tb of data overs hard drives usbs etc. so far.

The mac version of Witcher 2 is humongous, and the REDKit development archive is over 4GB. The windows installer files should be 4GB or less, thus able to be copied to a FAT32 drive, though without the extra NTFS streams.
Edit: typo

the witcher 2 files are 1,5 gig each
but there are 13 of them

beyond good and evil is 1,5 gig on its own i doubt fat 32's upper limit is the issue here

It sounds like NTFS file stream information is being lost when copying over to fat32 (this is usually just a warning and the files copy fine, just without some usually optional info). But I dunno what GoG would be storing in the file streams If they are, and it can't be that helpful because all my games are stored exclusively on btrfs in linux, so all that same stuff would have been stripped on my copies as well.

FAT32 is the problem, not due to file size, but because NTFS supports alternate data streams that FAT32 doesn't support. For more info, take a look or [url=http://en.wikipedia.org/wiki/NTFS#Alternate_data_streams_.28ADS.29]here. They are not. It's most likely the zoneidentifier ADS added by the browser.

They're not, NTFS has additional properties such as ACL (Access Control Lists, permissions basically).
It's a bit like saving a Word document as a text file, you lose the formatting but the core remains the same.
That's what I think at least.

Ah yes. I forgot about that thing. Yeah I think you're right.

Which doesn't matter, because the 4GB filesize limit is per file (I would think that to be obvious, but then, I'm a geek), not total. FAT 32 has no problem handling a full drive up to 2TB, as long as no single file is larger than 4GB.

It doesn't matters, you can copy them without properties. And yes FAT32 has a per file limit of 4GB and most USB sticks are formatted to FAT32 by default.

If the drive is 2GB or less, it might be FAT16... If it's a Gig or less it could possibly be FAT12. (blocksize maxed at 64k)