Here is the solution:
The problem isn't that the folder is Read Only. Rather, because your folder was created on a different
installation of Windows you no longer have NTFS security permissions to access (read) the folder.
Correct this by following these steps to take ownership and then grant yourself full access to the folder.
1.Right-click the folder > Properties
2.Security tab > Advanced
3.Click Change to the right of Owner
4.Enter Users (user name you used when installing Windows) into box and click check names then OK
5.Enable the checkbox Replace owner on sub-containers and objects then click Apply
That should fix it at this point item 5, however see below if problem continues:
6.If prompted that You do not have permissions to read... click Yes
7.Completely close out of the Advanced Security Settings dialog
8.Right-click the folder > Properties
9.Security tab > Edit...
10.Add...
11.Enter Users into box and click OK
12.Enable the Full Control checkbox then click OK
Could you be looking at a SSD that's reached the end of it's rated life and gone into read-only mode? – Loren Pechtel – 2013-08-01T18:10:56.267
The question is inconsistent, saying you remove readonly from the folder, but then your title is about files. Folders in Win 7 can show in File Explorer as "Readonly" (a black square vs a checkmark means that only some of the files underneath that folder are Readonly) but that doesn't actually mean all the files are Readonly. Pls clarify the question to address 1) What folders are you looking at; 2) How are you seeing the Readonly box (File Explorer, right-click folder & choose Properties ?), and 3) Whether you are checking files or just folders. This type of detail is important. – Debra – 2019-01-16T22:15:33.433
Have you considered opening up process monitor and seeing who's setting the readonly bit? – Billy ONeal – 2011-01-31T01:51:50.783
can you give details?, I am using windows in another language, so I couldn't find the process monitor, do you mean ctrl + alt + del ? – sprsr – 2011-01-31T12:29:11.893