From: João Ribeiro KS (
Date: Tue Mar 07 2017 - 17:25:26 CST

Dear Kanishk,

The" Localhost port 3000 error" is just a message of VMD saying that it
could not establish a connection to NAMD, but will try again. You just have
to wait long enough to connect (NAMD starting process), specially in
explicit solvent systems. An error window will pop-up if the connection is
definitely refused.

The problem is if some error appeared before the messages of "Localhost
port 3000 error" started to appear. Do you see any error before these

If the connection is never successful, you have to change your firewall
definitions, on Settings/System Preferences, "Security & Privacy". You can
find more information here:


Joao Ribeiro

On Tue, Mar 7, 2017 at 5:08 PM Kanishk Jain <> wrote:

> Hello all,
> I'm an MD novice, starting out on QwikMD. I'm using a mac with the
> following versions of VMD and NAMD, respectively: vmd193macx86nocuda
> and NAMD_2.12_MacOSX-x86_64-multicore-CUDA.
> My problem is that when I try to start a simulation, I keep getting the
> following error:
> ERROR) Error connecting to localhost on port 3000
> I've seen a similar question to mine as it applies to Linux machines, but
> as I'm a novice, I'm not quite sure how to implement the solutions
> mentioned in those threads to my situation. Any help would be appreciated!
> -Kanishk
> --
> Sincerely,
> Kanishk Jain
> Steven G. Clarke Laboratory, PhD Candidate
> Biochemistry and Molecular Biology Program
> Department of Chemistry and Biochemistry
> University of California, Los Angeles

João Vieira Ribeiro
Theoretical and Computational Biophysics Group
Beckman Institute, University of Illinois
+1 (217) 3000380