The issue : When selecting Export to XML under Related Links for a Local Update Set, the link does not appear to work. The page goes white and there is no download available. I tried this on multiple completed update sets, to rule out if file size was the issue. I can export to xml via right clicking on the form, its the link on the form that does not work.

The solution, as directed by HI per KB1116189

1. Navigate to sys_ui_action.LIST and search with Name 'Export to XML' 
2. Open record 'Export to XML 'where Table is 'Update Set [sys_update_set]'
3. Click on Version tab and sort by Recorded at.
4. Open first record in the list
5. Click 'Revert to this Version' related link.