Don't know. Have never seen this.
Can you use a workaround? Create it 'in your account' then using the mouse MOVE it to the folder you want to have it in? That works with me. But if something is wrong with your OE, it's possible that it doesn't work with you either. But it's worth a try.
I cannot create subfiles within files EG within my new post or sent post files. When I right click to go to the new file option I get the box for creation with the line to insert the name you want to give the file but the OK button is not active.
I can only create new files within the same account.
I am using a Sony Vaio (never again) with Microsoft Windows XP version 2002