Can't see hidden folder in Finder, but “ls” and “cd” work

Question

On my external hardisk there are two folders inside a folder called "Sys". When I try to navigate to "Sys" using Finder (using "go to folder" option), I only see one folder inside "Sys".

When I use terminal to navigate to "Sys" folder and execute the command ls -ltr I can see both the folders and can also cd into them.

I also did:

defaults write com.apple.finder AppleShowAllFiles TRUE
killall Finder 

But the second folder is still not visible in Finder, and I also cannot navigate to it using Finder.

EDIT:the output of ls -ltr

  drwxrwxrwx@  5 net4uonline  staff   170 Aug  3  2009 Installation
  drwxr-xr-x  32 net4uonline  staff  1088 Aug  3  2009 Library

and for ls -l@

 rwxrwxrwx@  5 net4uonline  staff   170 Aug  3  2009 Installation
    com.apple.FinderInfo      32 
 drwxr-xr-x  32 net4uonline  staff  1088 Aug  3  2009 Library

Installation is the invisible one.

Answer 1

Seems like the folder has the hidden flag set? It should be visible when you do a ls -lO. Try

chflags nohidden /Volumes/your-drive/Sys/Installation

and see if that resolves the problem. You should always be able to open the folder in Finder with open Installation.