777 Is an indication of a folder with all permissions on a Unix (like) system (7 = read, write and execute and in order user, group, world).
Windows do not have the same permission system and it is therefore not possible to set a folder's permissions to 777 in Windows. The normal right mouse click, then properties in Windows Explorer should take you to the permissions of the folder. You would need to ensure that this is not read only. Depending on you Windows version and the file system it use eg NTFS it would be able to set other access attributes.