I also find my sitemap has not cokmpleted it's daily run. I get a notice like this:
* The last run didn't finish! Maybe you can raise the memory or time limit for PHP scripts. Learn more
* The last known memory usage of the script was 47.75MB, the limit of your server is 64M.
* The last known execution time of the script was 122.41 seconds, the limit of your server is 120 seconds.
But when I then run it manually, it gives me this ntoice of successful completion:
# Your sitemap was last built on October 30, 2009, 8:31 am 8:31 am.
# Your sitemap (zipped) was last built on October 30, 2009, 8:31 am 8:31 am.
# Google was successfully notified about changes.
# Bing was successfully notified about changes.
# Ask.com was successfully notified about changes.
# It took 8.28 seconds to notify Ask.com, maybe you want to disable this feature to reduce the building time.
# The building process took about 10.12 seconds to complete and used 40.75 MB of memory.
Why would it work on manual, and not when running in auto?
I'm on 2.8.5 and 3.1.7 of the plugin. It's been doing this on ealier releases as well.