I'm going to jump in here with the same problem. ERA 6 Server on CentOS VM (Appliance provided from ESET, ESXi), and the Server is on the domain. Attempting to deploy the agent gave the same errors as the OP. I verified that the unit was on the domain. While looking at the logs, I noticed the timestamps were off... which made me think about the timezone... which turned out to be set incorrect.
Correcting the timezone fixed the deployment to some PC's but not others. On the others, I was getting a mount error(12): cannot allocate memory. These computers are 4 year old Dell's that only have 2Gb RAM, and apparently there is a Windows 7 glitch regarding cifs shares regarding memory. To resolve that you need to do the following on each unit:
reg add "HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v "LargeSystemCache" /t REG_DWORD /d 1 /f
reg add "HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters" /v "Size" /t REG_DWORD /d 3 /f
NET STOP LANMANSERVER /Y
NET START LANMANSERVER /Y
I got the above from : https://wiki.archlinux.org/index.php/Samba/Troubleshooting
I put this in a batch file that I could deploy with PDQDeploy when needed.
One request to Eset Development - Better error messages in the Web GUI, the only messages I have gotten are Task Failed with the Generic troubleshooting steps.