This issue may be caused by broken, corrupted credit links by your email software.
Besides, have in mind that to earn credits you must remain on the site for 15-20 seconds or until the top message changes to something like "You were credited by 80 credits" .
Some of the members overlook this rule and as a result appeal to the admin for the fix.
You might have also opened too many credit links simultaneously in your browser
or use some Auto Hit Bots (clicks generating software).
Make sure you read this item of the FAQ: