Maybe the content didn't have a proper copyright:
From the Fanpop Terms and Services:
link
- You understand and agree that Fanpop may review and delete any Content (Fanpop, links, images, profiles, comments, postings, messages) that in the sole judgment of Fanpop violates these Terms of Service or which might be offensive, illegal, or that might violate the rights of, harm, or threaten the safety of other users or members of the Fanpop Site and/or other website users.
- You may not post, distribute, or reproduce in any way any copyrighted material, trademarks, or other proprietary information without obtaining the prior written consent of the owner of such proprietary rights.
Also, did any of the content fit this criteria:
The following is a partial list of the kind of Content and communications that are illegal or prohibited on/through the Fanpop Site. Fanpop reserves the right to investigate and take appropriate legal action in its sole discretion against anyone who violates this provision, including without limitation, removing the offending communication from the Fanpop Service and terminating the membership of such violators or blocking your use of the Fanpop Service and/or Fanpop Site. You may not post Content that:
is false or intentionally misleading;
- is patently offensive to users of the Fanpop Site, such as Content or messages that promotes racism, bigotry, hatred or physical harm of any kind against any group or individual;
- harasses or advocates harassment of another person;
- involves the transmission of unsolicited mass mailing or "spamming";
promotes illegal activities or conduct that is abusive;
- is threatening, obscene, defamatory or libelous;
- is pornographic or sexually explicit in nature; and
seeks or recommends providers of material that exploits people under the age of 18 in a sexual or violent manner, or seeks or recommends providers that solicit personal information from anyone under 18.
If you were not notified of the reason for the removal in a e-mail or other, then you should probably notify the Owners of Fanpop. It may be a mistake.
