Generating a User Report for one email address (one user) for any time period takes a long time and eventually times out. Regular reports for all users are generated successfully.
GFI MailEssentials 2012 build 20120913.
A report for one user has more criteria to define than a site-wide report. As the query is more complicated, it takes more time to complete and eventually times out if the dataset is too large.
Upgrade to GFI MailEssentials 2015 or later.