While running Maple (13.0 and 13.02) on a Linux system that has IPv6 enabled (Debian Sid AMD64 as of December 8, 2009) I found that the xmaple interface was unable to connect to the Maple kernel.  Command line maple worked fine with a simple test of 2 + 2.  Xmaple had some odd behavior as the kernel connection issue is not reported until running a calculation.  Aslo I found the many of the menu items were dimmed out such as "Help" -> "About" and "Help" -> "Maple Help."  Further selection of the "Tools" menu caused the interface to freeze forcing me to kill the xmaple process externally.  After a bit of searching I found an old post in the fedora-list@redhat.com listserv that indicates Java may have issues with IPv6:

http://linux.derkeiler.com/Mailing-Lists/Fedora/2005-07/2472.html

For Maple 13.02 I changed line 68 of /maple13/bin/maple from:

JVM_OPTIONS="-Dsun.java2d.pmoffscreen=false"

to

JVM_OPTIONS="-Djava.net.preferIPv4Stack='true' -Dsun.java2d.pmoffscreen=false"

This has resolved the problem for me.  I thought I'd report the experience here as a MaplePrimes Blog entry to seed the search engines.  Hopefully others who experience this problem will find this one-line change helpful.

Debian Bug Report 560142 relates the net.ipv6.bindv6only parameter in /etc/sysctl.d/bindv6only.conf to the troubles with Java.  To handle the general case of Java-based applications it may be neccessary to modify this file.