I have Ubuntu 12.04.1 64-bit and encountered a problem with LibreCAD regularly (nearly always) crashing when trying to open a .DXF file by selecting it from the File>Open dialogue window.
The symptoms seemed to be more or less identical to those described in the thread started by gee on May 22nd 2013.
I tried both version 1.0.1 from the Ubuntu repositories and also 2.0.0rc1 from the daily builds ppa with the same results.
Running LibreCAD from a command line in a terminal would produce the following output just prior to the crash :-
Interface is not valid
ASSERT failure in : "Got an update for an invalid inteface. Investigate this.", file atspiadaptor.cpp, line 899
After a bit of searching, this led me to this bug associated with the package qt-at-spi affecting a number of applications including LibreCAD :-
https://bugs.launchpad.net/ubuntu/+source/qt-at-spi/+bug/998012I removed the package qt-at-spi as suggested in the bug report and this now seems to have resolved the issue.
The package qt-at-spi is intended to provide Qt related support for Accessibility features such as Orca Screen Reader - something that might need to be considered before removing it.
I hope that the above information may be helpful to others encountering the same problem.
Regards
Stephen