I have asked the sitemap authors and they are getting back to me, no server issues and plenty of memory as i have a VPS, hosts say "It seems that mysql does not have enough memory to store the entire query result.
Please make sure that your query is correct. More information about this issue you can find
on the following pages:

https://dev.mysql.com/doc/refman/5.0...of-memory.html
http://forums.mysql.com/read.php?37,94800,190727
"

was working till a thursday last week. I posted in both as this mod was listed.
Thanks