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:
http://yourdomain.com/wp-content/plugins/custom-tables/dl.php?i=1&l=953923c20A49c-d244a9a5eae2za7Sc9&t=csv

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

http://yourdomain.com/wp-content/plugins/custom-tables/dl.php?i=1&l=953923c20A49c-d244a9a5eae2za7Sc9&t=csv&d=true

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