StumbleUpon Adsense Ban

I use Firefox, so here's how to remove in that browser:
Tools > Add-ons > click on StumbleUpon and then click Remove

But, you CAN delete your StumbleUpon account by reading here:
http://help.stumbleupon.com/customer/portal/articles/665202-account-settings#article17

http://www.downforeveryoneorjustme.com/ says it must just be you.

I had the same problem in both Firefox and Internet Explorer. I discovered that the problem was caused by my Kaspersky Internet Security software.

Specifically, in the Content Filtering section I disabled the Banner Ad Blocker and the problem disappeared.

based on this
http://www.whois.ws/whois-ip/74.201.117.232/

NetRange: 74.201.0.0 - 74.201.255.255
CIDR: 74.201.0.0/16

so you need to block those set of ip addresses via .htaccess.
once you do this other sites hosted on those ip address can't access your site.

if you have existing .htaccess file better download that your computer first then add the lines:

order allow,deny
deny from 74.201
allow from all

if not existing:
create a file .htaccess

the content of the .htaccess file is this:

order allow,deny
deny from 74.201
allow from all

my suspect is firefox3 is conflicting with one of your ff add-ons, or stumbleupon is conflicting with one of your firefox 3 add-ons.

isolate the problem, one by one disable the add-on and try what you can't do before, see if it works.

Look at this:

http://www.stumbleupon.com/help/#changepassword

assumed resolved issues.

The toolbar is the problem, Re install the StumbleUpon toolbar, and your problem will be solved.

try this url
http://www.stumbleupon.com/url/www.domain.com/

replace www.domain.com with your actual url

if you thumbs up a site and no one reviews it, no one stumbles it via reply then it's graveyard
to summarize the read below, you can't avoid getting your site there, since this is a decision of the whole community of stumbleupon members and can't be manipulated by one person only.

http://blog.venture-skills.co.uk/2008/02/08/stumbleupon-graveyard/