I added a user to a group and set the file and dir content to 775. When i use winscp to modify a file it complains it cant set the timestamp bc of a permission error. But it is able to update the file i edit. Why? details on how i set the user is here but i dont think anyone needs to read it http://serverfault.com/questions/159179/why-cant-a-group-member-modify-a-file-in-a-group-he-is-part-of
I guess your directory has the wrong owner/group, though the file itself has. What WinSCP is probably complaining about is that it can't set the directory’s timestamp, which is normally also updated if you change a file in it.