Backup/Export show only white page

If you only see a whit page if you want to export a table or take a backup, then login to the WordPress Admin Menu and navigate to the Export/Import or Backup/Restore Page.

Click on the CSV Export.
A new Window is open with the link like:

Attach the String ‘&d=true’ to the end and reopen page:

Afterwards you get some Text output.
Please send me this code.