Sitemap Regenerate Button Progress Bar Freezing

I have two urls running from same admin panel one is set up as an alias. When i try to regenerate the site map through Admin - Manage Add-ons - Google sitemap for the alias url the progress bar moves to about the middle then stays there.

Any ideas why this is happening?

The other url re generates the site map with no problems.

This can be timeout issue. Start from checking error logs on your server

Thanks for the reply.

Went back and tried the re gen site map which went ok so not sure why it was timing out.