Cannot delete all contents of Outlook Secure directory

Hello,

I've seen the problem with not being able to open attachements in the past -
empty out the Outlook Secure folder and then all is well.

However, this time it won't let me remove all the files in the directory.
Anyone seen this same problem? First it tells me that it's read-only and then
it won't let me delete it. How can I fix this problem?

The error I'm receiving when I attempt to open the attachment is:

Unable to open file <path to Outlook Secure Folder\filename>. Check file
name and permissions.