Problem with signing an update

Hi all,

when initiating the update process first all looks fine. The download begins, but afterwards a second alert pops up, indicating an "The update is improperly signed"-error. I tried since hours, following strictly the instructions in the documentation, but still have no idea what is wrong.

Only one detail: when I sign the update with the Ruby script I always get a 2 line signature with a line break in between. I tried this a number of times, also with new created public and private keys but it always looks similar. I entered this signature in different ways in the appcast.xml but it never worked. (2nd line only, both lines without line break and with line break). For instance:

ruby "Extras/Signing Tools/sign_update.rb" ~/Desktop/MyApp.zip ~/Desktop/dsa_priv.pem
MEUCIAonkjhUhVaZdGEIcb99qVTL9PboM/yrLUAh/ugC6QIcAiEAiTLU/oyijrAQ
ak41RwMfxMyB1dCaJb5exJ6N5smwXwQ=

My appcast.xml looks like that:

<?xml version="1.0" encoding="utf-8"?>
<rss version="2.0" xmlns:sparkle="http://www.andymatuschak.org/xml-namespaces/sparkle" xmlns:dc="http://purl.org/dc/elements/1.1/">
   <channel>
      <title>Trinity Changlog</title>
      <link>http://rhodesit.min.uni-kiel.de/~pa/appcast_tri.xml</link>
      <description>Most recent changes with links to updates.</description>
      <language>en</language>
         <item>
            <title>Trinity Version 1.7</title>
 <sparkle:releaseNotesLink> http://rhodesit.min.uni-kiel.de/~pa/trinity.html</sparkle:releaseNotesLink>
            <pubDate>Thu, 21 Oct 2010 20:20:11 +0000</pubDate>
            <enclosure url="http://rhodesit.min.uni-kiel.de/~pa/pub/software/Trinity.zip"
            sparkle:version="1.7"
            length="616466"
            type="application/octet-stream"
            sparkle:dsaSignature="ak41RwMfxMyB1dCaJb5exJ6N5smwXwQ="
             />

         </item>
   </channel>
</rss>

I'm using SL 10.6.4, with the latest Sparkle 1.5 b6.

Any help is greatly appreciated!
Thanks,
Peter