There is a known issue on XP and possibly other Microsoft Windows versions that if you are running their early version of their Java then you can have crashes in live Thud when sending messages in the message windows at the same time as others.
The only know fix at the moment is to upgrade to latest Sun Java version.
http://www.java.com/en/download/index.jsp
If you still have problems please post detailed description of how crashes happen in this forum with computer type (PC/MAC/Other)/Operating system(Win 95/98/2K/XP : Linux ver : MAC 10.x) and version no. of Java if known. As this will be helpful to the developers of future versions of the software.