Looking at the page the most likely cause is the memory allocated to PHP has been exhausted causes PHP to stop running. My suggestion is to try increasing this amount. Try 128MB.
See this excellent blog post on how to do it. Since every host is different, which method that will work is unknown. My suggestion would to be start at the top and work your way until the issue is, hopefully, resolved.
Let me know how you make out.
Oh, any reason, could be
Try increasing this too.