I had a similar problem once with pine.. Kept complaining it couldn't lock the
mailbox and was unable to delete mail.. Checked the permissions a hundred
times.. they were fine.. It turned out the user couldn't write to the /tmp
directory, and that was what screwed it up.

No idea if that is the same problem you are seeing..

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Tim Rightnour    -  root@garbled.net
http://www.zynetwc.com/~garbled/garbled.html