How to avoid "Invalid Trajectory (cost: -1.000000)" in DWA Local Planner?

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Dear all,

I am using DWA to drive a differential robot around. I am running Ubuntu 12.04 and ROS Hydro.

In general, the robot navigates well. However, sometimes when I send it to tight spots, I receive the following warnings:

[ WARN] [1435079055.081046415]: Invalid Trajectory 0.000000, 0.000000, 0.822608, cost: -1.000000
[ WARN] [1435079056.578828210]: Invalid Trajectory 0.000000, 0.000000, 0.931650, cost: -1.000000
[ WARN] [1435079058.079198312]: Invalid Trajectory 0.000000, 0.000000, 0.850638, cost: -1.000000
[ WARN] [1435079058.580604641]: Invalid Trajectory 0.000000, 0.000000, 1.000000, cost: -1.000000
[ WARN] [1435079060.483851910]: Invalid Trajectory 0.000000, 0.000000, 0.400000, cost: -1.000000

While receiving these warnings, the robot stands still, and eventually starts doing recovery behaviors, aborting most of the time afterwards.

My questions:

• What is causing these invalid trajectories with cost: -1?
• How can I avoid them?

Below, my "base_local_planner_params.yaml" file:

TrajectoryPlannerROS:
  max_vel_x: 0.8        
  min_vel_x: 0.2
  max_vel_y: 0.0        
  min_vel_y: 0.0  
  max_vel_theta: 2.0
  min_vel_theta: -2.0 
  min_in_place_vel_theta : 0.65
  escape_vel: -0.1

  acc_lim_theta: 3.2    
  acc_lim_x: 2.5        
  acc_lim_y: 0.0                       

  holonomic_robot: false

  sim_time: 1.5
  sim_granularity: 0.025 
  angular_sim_granularity: 0.025
  vx_samples: 5                         
  vy_samples: 0
  vtheta_samples: 20
  meter_scoring: false                 

  yaw_goal_tolerance: 0.2              
  xy_goal_tolerance: 0.25              
  latch_xy_goal_tolerance: false        
  gdist_scale: 0.5                      
  pdist_scale: 0.7                      
  occdist_scale: 0.02        

  dwa: true

Here is a video of the robot's behavior: https://youtu.be/Y-zro-sXO-o

Let me know if further details are necessary. Thanks in advance!