Better handle plugin exceptions.

Cura/gui/sliceProgessPanel.py

@@ -168,7 +168,9 @@ class WorkerThread(threading.Thread):
 				if logLine.startswith('Model error('):
 					gcodefile.write(';%s\n' % (logLine))
 			gcodefile.close()
-			profile.runPostProcessingPlugins(gcodeFilename)
+			ret = profile.runPostProcessingPlugins(gcodeFilename)
+			if ret != None:
+				self.progressLog.append(ret)
 			self.gcode = gcodeInterpreter.gcode()
 			self.gcode.load(gcodeFilename)
 			profile.replaceGCodeTags(gcodeFilename, self.gcode)

Cura/util/profile.py

@@ -612,7 +612,12 @@ def runPostProcessingPlugins(gcodefilename):
 				try:
 					value = float(value)
 				except:
-					value = 0.0
+					value = float(param['default'])
 			
 			locals[param['name']] = value
-		execfile(pythonFile, locals)
+		try:
+			execfile(pythonFile, locals)
+		except:
+			locationInfo = traceback.extract_tb(sys.exc_info()[2])[-1]
+			return "%s: '%s' @ %s:%s:%d" % (str(sys.exc_info()[0].__name__), str(sys.exc_info()[1]), os.path.basename(locationInfo[0]), locationInfo[2], locationInfo[1])
+	return None