[horde] Cannot export IMAP folder to MBOX

[Louis-Philippe Allard]

Hello maillist

I am trying to export a GMAIL IMAP folder to an MBOX file.  I right  
click on the folder, and select "Export" then select "Download into a  
MBOX file".

The server works for a few minutes then Firefox throws a page saying

************************
File not found

An error occurred during a connection to hordemail.

    Check the file name for capitalization or other typing errors.
    Check to see if the file was moved, renamed or deleted.
************************

Horde.log has nothing relevant in it.

What is causing this?
  Louis-Philippe Allard
lp.allard.1 at gmail.com
Sent using Horde Groupware on GNU/Linux