tmpwatch deleted an iso image in /tmp WHILE it was mounted at /mnt/cdrom via loop device.
Change the tmpwatch policy (probably by disabling) if you're going to put unusual things in /tmp. There's no (easy) way that tmpwatch can discover that a file is in use.
I have to respectfully disagree with this. While in this instance, I was making an unusual use of /tmp, there are a number problems with not checking whether the file is open before deleting it. As more and more commercial software is developed for Linux, /tmp may be used in ways not expected. Even free software may use /tmp in ways you don't expect. For example, Meta-HTML (www.metahtml.org) is a web-server which puts its session database in /tmp by default. Of course, once tmpwatch deletes it, it continues to work ... but none of the other utilities designed to access the session database will work. While it may in INCONVENIENT to fix this, I doubt that it is difficult - the code is in lsof.
we have added a flag to use fuser to determine whether a file is open or not for 6.2. However, this option is turned off by default.