Files missing from export and empty .zip file

When I export my site files, the zip file is empty, similar to this post: http://wordpress.org/support/topic/plugin-wp-static-html-output-generated-zip-file-is-empty-what-am-i-doing-wrong?replies=2

If I use my custom theme, Export Log always ends at the same file (about 60% through), meaning I’m missing about a third of the static page content. If I change to the default theme, the core files are fine, but this is not the theme I need to generate. In both cases, the zip file is blank.

How do I make sure my custom theme can be used to export all files? Is there a log I can inspect for more detail? (this question was unanswered in the original post). Is there some taboo block of PHP or JavaScript code I should avoid in my custom theme that might be causing this whole mess?

Thanks.

http://wordpress.org/plugins/static-html-output-plugin/