I see you are using tomcat 7.0.28 - probably your are still on wheezy?
There are some bug reports for that message; it seems upgrading tomcat helps, e.g.:
http://stackoverflow.com/q/23541532
http://stackoverflow.com/q/23484098
However the tomcat with wheezy is just too old:
https://packages.debian.org/wheezy/tomcat7
The tomcat with jessie should work
https://packages.debian.org/stable/tomcat7
Maybe try "wheezy-backports" if you do not want to update to jessie
(I have never done that myself, so I cannot be of much help here)
Alternatively it might help editing xwiki's web.xml manually by adding a
metadata-complete="true"
as suggested here:
http://stackoverflow.com/a/12730059
though I have not tried this and do not really understand why it should help
HTH
Clemens
----- Ursprüngliche Nachricht -----
Von: Stéphane Lassire
Am:  Wednesday, 25.05.2016, 12:48
An: Xwiki Users
Betreff: Re: [xwiki-users] Error upgrading Debian
  Hello Thomas,
 The answer :
 root@CESAP-WIKI01:/var/log/tomcat7# ps aux | grep tomcat
 tomcat7   6355  7.3  6.7 2182572 275136 ?      Sl   12:34   0:59
 /usr/lib/jvm/java-8-oracle/bin/java
-Djava.util.logging.config.file=/var/lib/tomcat7/conf/logging.properties
  -Djava.awt.headless=true -Xmx512m -XX:+UseConcMarkSweepGC
-Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager
  -Djava.endorsed.dirs=/usr/share/tomcat7/endorsed -classpath
 /usr/share/tomcat7/bin/bootstrap.jar:/usr/share/tomcat7/bin/tomcat-juli.jar
 -Dcatalina.base=/var/lib/tomcat7 -Dcatalina.home=/usr/share/tomcat7
-Djava.io.tmpdir=/tmp/tomcat7-tomcat7-tmp
 org.apache.catalina.startup.Bootstrap start
 thanks for the help
 Cordialement
 Stéphane Lassire
 -----Message d'origine-----
 De : users [mailto:users-bounces@xwiki.org] De la part de Thomas Mortagne
 Envoyé : mercredi 25 mai 2016 12:46
 À : XWiki Users
 Objet : Re: [xwiki-users] Error upgrading Debian
 "Invalid byte tag in constant pool: 15" still looks like a Java version
 issue.
 Could you check what version of Java started with "ps aux | grep tomcat" ?
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