Starting Mach4 with ESS plugged in, I get the message "CTftp::WakeUpClient - Error in recv"
Mach4 v4.2.0.5036
ESS plugin v285

Things I've tried:
System Configuration Utility - everything goes smoothly AND I get ping responses.
Ran Configurator to reset ESS to 10.9.9.9
Firewall seems to be configured properly, but to be sure it was not the problem, I have turned it OFF
Web searches for the error message turn up nothing particularly useful.

Hi, I found this note on the ESS website..

"NOTE!!!! Build 5000 is having probing issues with the ESS plugin... Mach4 Build 4809 with ESS 283 is what we are recommending at the moment. January 15th, 2023"

Yea, I saw that - figured that Mach version was 36 versions old and the ESS plugin has had 2 revisions since then, so wouldn't expect that reccomendation to still hold.  Hoping to hear from Warp9...

I want to try the 4809 build, but can't find anything other than the latest 5036 build to download... where do I need to be looking?

You can download build 4809 from the Warp9TD website here;

https://warp9td.com/index.php/gettingstarted/setting-up-the-smoothstepper-and-mach4#SetupInstallEssPlugin

Tweakie.

Have now tried:
Mach4 v4809 with ESS v285
Mach4 v5036 with ESS v285
Mach4 v5036 with ESS v296
All produce the same error message: "CTftp::WakeUpClient - Error in recv"

I thought that this might be an error being thrown by the Ethernet communication layer in Mach4, so I began to wonder if there is incompatibility with my Ethernet driver.  After finding that HP and Intel both offer no other driver, and Windows indicates that it is the latest driver, I thought to try another tack and plugged in a USB/Ethernet adaptor.  That adaptor was seen by the Warp9 SCU, initiated, and responded to pings.  On startup of Mach4 I still get the same error message. 

Are the Newfangled Solutions guys at all active on this forum?  Anyone who could be invited in to this thread?

You said you configured the firewall.
Try turning them off.
Also, you must cycle the power on the ESS after a failed attempt at communication.

Also, it is not Newfangled you need to help.
Contact Warp9
https://warp9td.com/

Thanks Bill

Firewall is OFF (as per OP)

I have not always cycled power on the ESS between all attempts - good to know - I did some re-testing to verify, but still get the error every time.

Sometimes I need to step back... re. contacting warp9 to get to the bottom of this - you're thinking that the ESS Plugin is what is handling the Ethernet communications and the source of the error message?

Has anyone had any luck contacting someone at warp9?  They have not responded to posts on their forum...

I have always found them to be very responsive if contacted directly.
support@warp9td.com