Thanks for the information. It seems like the update has caused the problem. Possibly an update to an incompatible version of glibc or another library.
Can you please let me know what package of QCAD you have installed, the regular Linux package or the one with -alt in the package name?
You might also want to try the current development snapshot ( 3.0.8 ) available from your download area. It ships with its own version of glibc which might fix the problem.
To download QCAD 3.0.8, please follow our instructions at:http://www.ribbonsoft.com/en/customer-area
Then scroll down to "Development Snapshots".