My console is filling up with these errors and I'm getting "too many open files" errors, and I'm unable to perform any actions at all.

When the errors began last week, I was able to boot into -s mode, manually mount and fsck the slices, and add the following two kernel paramenters to /boot/loader.conf to get me back up and running:
kern.ipc.maxpipekva: 8634368
kern.ipc.pipekva: 344064

However, after trying a few intensive operations yesterday, such as cvsup, the errors came right back and do not desist unless I reboot the machine. They then reappear after a few minutes, even if the system is idle and I don't even log in after reboot.

Is there a recommended value for these parameters if I've got a total of 340MB RAM, or another way of solving this problem? Google gives lots of hits but really no definitive answers (same for a post on this forum).

Thanks for your help.

There is probably more information in your log file. Not just what spills over into the console where is generally only kernel errors.

Probably... problem was, there were so many open files, I couldn't get any commands in.

Rebooting and changing the value of "openfiles" from "unlimited" to "1024" in /etc/login.conf seems to have solved it for me. I don't know if that number is too large or small, but it's working so far.