Load directory tree failed

I have a directory containing 40.000 xml document, I tried to import this
directory into the Xindice:

xindiceadmin import -c /db -f tmp -e xml -v
Created : /db/tmp
ERROR : Java Runtime Error
ERROR : null
java.lang.NullPointerException
        at
org.apache.xindice.tools.command.AddDocument.execute(AddDocument.java:150)
        at
org.apache.xindice.tools.command.ImportTree.importFile(ImportTree.java:189)
        at org.apache.xindice.tools.command.ImportTree.process(ImportTree.java:167)
        at org.apache.xindice.tools.command.ImportTree.execute(ImportTree.java:118)
        at org.apache.xindice.tools.XMLTools.execute(XMLTools.java:331)
        at org.apache.xindice.tools.XMLTools.process(XMLTools.java:257)
        at org.apache.xindice.tools.XMLAdminTools.main(XMLAdminTools.java:89)

I tried to import a directory containing 5 files and it worked
I tried to add multiple document using the following command:
xindiceadmin add_multiple_documents -c /db/book -f tmp
after 5000 file, it reported "ERROR: Too many open files"

I hope you can help...
Thank
Amir Saad
Software Engineer