The "class "com.lowagie.text.pdf.BadPasswordException"'s signer information does not match signer information of other classes in the same package" error means two or more libraries use the same package. The Eclipse BIRT's com.lowagie.text plugin, that is signed, is one of them. Java doesn't allow two libraries to use the same signed package.
Check the WEB-INF/lib directory. I suppose you have two versions of this plugin (from two BIRT versions, probably).