Hi Paul
This could be because some of the ping services is not working OK. Please try disabling some of them, specially technorati, because when it takes some time to send the ping, your php/apache can generate a timeout and thus a error 500.
In the plugin configuration there is a list of services, just check for the technorati url and delete it, leaving only the pingomatic and google. If this don't fix your problem try removing others. The one that always work is google

so if you remove all of them and let google be the only one, and the error continues, please check your log files to see if there is another error.
PS: save the addresses you delete to restore them
Paul wrote:
Hey,
Firstly, great plugin
At the moment I'm having some troubles, every time I add a new article or edit an article and hit save/apply I get a 500 Internal Server Error.
I'm using Xmap to generate a sitemap, and I have turned off "Create sitemap" option. In the field called "other sitemap" I entered this /index.php?option=com_xmap&sitemap=1 before I also tried with domain name put in.
Yahoo is set to No and everything else underneath is set to Yes.
Is there something I can do?
Please be gentle I'm a basic joomla user 
Thanks,
Paul