OK, we have hit this one a couple of times when a fold copy has not completed for some reason and unless you know how to fix this then you will not be able to access the folder and potentially lose the files within it.
A greyed out folder on a MAC is often caused by a creation date problem on the folder, the first obvious thing you can do is reboot and see if it sorts itself out, if not there are a few other ways to get back into a greyed out folder on a MAC.
One way is to use the terminal to rename the folder, then create a new folder and move the content of the original to the newly created folder, simple enough to do using the command line terminal.
From the Terminal Rename the Original Folder:
# mv MyFolder TempFolder
Then Make a new one and move the files from the old one to the new one:
# mkdir MyFolder # mv TempFolder/* MyFolder
And Your sorted, you now have a shiny new folder with the same name as the old one with all your files in it, all that is left to do is delete the old TempFolder.
The main problem with the above solution is it involved copying the data again, and this is what probably caused your issue in the first place, so much better to do a straight copy or tar the data:
# cp -pR TempFolder/* MyFolder/
or:
# (cd TempFolder; tar cf - . ) | ( cd MyFolder; tar xpf - )
However, given the main problem is usually the creation date of the folder being corrupt, a much faster and easier solution is to fix the original problem folder by setting the creation date into the past:
SetFile -d 02/02/2013 <folder_path>
And fingers crossed your sorted.
Doing It All Again 