Hello,
Could you please let us know what version of Kentico
CMS do you use, and what hotfix? Actually there was a bug which could be related. It has been fixed in 4.0.1 hotfix, therefore, if it's your case, I would recommend you to apply latest hotfix: http://devnet.kentico.com/Bugtracker/Hotfixes.aspx
Best regards
Ondrej Vasil