Problem while digitally sighning pdf using IText.

Hello all, I want to add a digital signature in pdf file containing singature field using Itext. i did as given in http://itextpdf.sourceforge.net/howtosign.html. but i always get following exception while loading the signature file. java.io.IOException: DerInputStream.getLength(): lengthTag=109, too big. can some one know, where is my problem? I am stuck over here. Any help will be appreciated. Regards Jaya N Pasachhe.