archive viewer installation problem

[Christophe Moins <moins@ego-gw.it>]

Hello,

I am trying to install archive viewer but I have the following message 
when I launch the ant command in  Archiveviewer's top directory :

***********************************************************************************************************
Buildfile: build.xml

-create_build_dir:

build_all:
   [javac] Compiling 842 source files to /root/archiveviewer/build
   [javac] 
/root/archiveviewer/src/epics/archiveviewer/base/AVBase.java:25: cannot 
access gov.sns.tools.messaging.MessageCenter
   [javac] bad class file: 
/root/archiveviewer/ext_jars/xal.jar(gov/sns/tools/messaging/MessageCenter.class)
   [javac] class file has wrong version 49.0, should be 48.0
   [javac] Please remove or make sure it appears in the correct 
subdirectory of the classpath.
   [javac] import gov.sns.tools.messaging.MessageCenter;
   [javac]                                ^
   [javac] 1 error

BUILD FAILED
/root/archiveviewer/build.xml:21: Compile failed; see the compiler error 
output for details.

Total time: 18 seconds
***********************************************************************************************************


Does anybody what's going on ?

Thanks
Christophe