If the tag diagnostics on the tags are not showing any error, then, your best bet is to implement a logger with a try…except structure.
Something like:
import java.lang.Exception
logger = system.util.getLogger("yourLoggerName")
try:
#script to attempt
except: java.lang.Exception, e:
logger.warn("An error occurred" , e)
except Exception, e:
logger.warnf("An error occurred: %s",e)
@pturmel has a PythonAsJavaException class in his later.py which will allow for more detail in the case of python exceptions