drive or unc share you are accessing is not available

what game/software?
what's your system?
if you aren't gonna bother listing other details, we have no idea and are clueless to help you, the things you have said could mean literally anything on a machine system, have u check the sub forms for the game, if it's a game issue.

Universal Naming Convention (UNC Path)

tl;dr - It literally means you need to make sure everything in the path is there or available to the system. Check the path. Drives can drop out or change places, and network shares can drop out.

Ex. \\host-name\share-name\file_path (and to the user it's x:\something\file_path)

EDIT: But yes, we need much more info than that...

https://www.google.fi/search?sxsrf=ALeKk00dc93LbzU_0MJTgaOFvEhXNx0Rlw%3A1590335953454&source=hp&ei=0ZnKXojOGZa43AOci4f4CA&q=drive+or+unc+share+you+are+accessing+is+not+available&oq=drive+or+unc+share+you+are+accessing+is+not+available&gs_lcp=CgZwc3ktYWIQA1CXCliXCmDZEWgAcAB4AIABd4gBd5IBAzAuMZgBAKABAqABAaoBB2d3cy13aXo&sclient=psy-ab&ved=0ahUKEwjI-s6M78zpAhUWHHcKHZzFAY8Q4dUDCAc&uact=5

https://answers.microsoft.com/en-us/windows/forum/windows_10-windows_install/error-message-the-drive-or-unc-share-you-selected/ed8ab443-b645-44be-9634-e1a9b5d9e063

So if this is about Galaxy installation failing, according to that try to uninstall old Galaxy from Windows Control Panel, then try to install again.

It often helps if you just google with the error message, like I just did.

In most cases you need to use an uninstaller to properly clean up remnants from previous installs as the built-in can't do it. If the install is broken it only spews out errors.

Maybe, I wouldn't know as I don't use Galaxy, but that guy in the second link apparently got his Galaxy installation problem solved by uninstalling remnants of old Galaxy installation, but the gist was he had to do it from Control Panel, and not from that newer Windows 10 something something place where you apparently can also uninstall applications.

Windows 10 is schizophrenic in that way, you can partly do the same things in different places.

Yes, it's rather funny and odd that way ;) BTW: I too fell for the same problem of not reading correctly; the difference is "you selected" vs "you are accessing" :D

OP's message indicate a pre-created path/share, not during an install.