In accord to Steve´s post check the permission of the .rsn file(s) in question.
Highlight the file,hit cmd+i and have a look in the sharing & permissions column if your account has "read&write" privileges.if not you´ve to change it by clicking on the little lock,enter your admin password
and alter it accordingly.
If there are more files you can do it one by one or the quick and dirty way.
Put all files which you can´t access into a folder and change permission of this folder like i described above w/ one addition.Click on the rack wheel and choose "apply to all enclosed items",confirm the dialogue by hitting enter and you´re done.
I reject your reality and substitute my own!