Unable to use drop box

I've got two computers contected over ethernet. Both running 10.4.5 however for some reason that I can't work out I am not able to drop something into the other computer's drop box. I get a dialog saying I don't have permission, what is even more strange is that I am able to open the other computer's drop box!

How can I fix this up. I ran sudo and repair permissions.

EDIT: more info

I connected to the other computer's spare admin account and that works as normal. That is I can't open their drop box, aslo the drop box that works normally has a little blue arrow on it but the drop box on the other account that won't let me drop into, has a yellow diamond on it.

 

OK I found the problem, it was caused by the other drop box permissions being 'read and write' instead of the default 'write only (drop box)'

I don't know how it got changed or why repair permissions didn't fix it.