Attachments remain in the Outlook Secure Temporary Folder

I'm having problems with attachments remaining in the Outlook temporary
folder.
I've emptied the folder but still it fills and they remain.
I've checked the registry setting as per KB817878
I've deleted the folder and Outlook has created a new on automatically and
added the registry entry.
But the problem persists.
This is happening on a number of PCs, but not all, on a small network.
Surely I'm not the only one who has encountered this problem.
Can anyone offer a solution?

Lester Bennett