Dear Abdullah,
Simulations using Veins run three programs in parallel: OMNeT++ runs
the network simulation, SUMO runs the road traffic simulation, and
sumo-launchd acts as a proxy between both. Consequently, the first step
should be finding out which program crashed.
Debug output for sumo-launchd can be found on the console, as well as
in its log file. Please refer to its --verbose and --logfile parameters
for controlling how much (and where) information is written.
Debug output for SUMO (both stdout and stderr) is captured by
sumo-launchd and stored in its log files (see above).
Finally, debug output for OMNeT++ can be found on the console
(immediately before the "simulation terminated" line). You can get more
in-depth information by enabling debug-on-errors and running the
simulation with a debugger attached (see below).
You can find more information on debugging at
http://veins.car2x.org/documentation/faq/
Best,
Christoph