Please note that you should include all those scripts in .MSI do not use general provided by Mike

Here is %SystemDrive?%\NSClient++\scripts content for remote update:

updatecmd.bat

@ECHO OFF
ECHO ======================================================== >> %SystemDrive%\NSClient++\install.log 
date /t >> %SystemDrive%\NSClient++\install.log 
time /t >> %SystemDrive%\NSClient++\install.log 
ECHO Downloading new flexsense agent... >> %SystemDrive%\NSClient++\install.log
%SystemDrive%
cd \NSClient++
ftp -i -s:%SystemDrive%\NSClient++\install\updateagent.txt <ftp_ip_address> >> %SystemDrive%\NSClient++\install.log
ECHO Done! >> %SystemDrive%\NSClient++\install.log
ECHO Installing/Upgrading new agent... >> %SystemDrive%\NSClient++\install.log
msiexec /i %SystemDrive%\NSClient++\install\flexsense.msi /quiet
ECHO Done! >> %SystemDrive%\NSClient++\install.log

updateagent.txt:

<user>
<password>
binary
get NSClient++.msi
bye

update.bat (command to be used as NRPE external script):

@ECHO OFF
if (%1) == () goto exit_usage
mkdir %SystemDrive%\NSClient++\install > NUL
copy %SystemDrive%\NSClient++\scripts\updatecmd.bat %SystemDrive%\NSClient++\install\updatecmd.bat 
copy %SystemDrive%\NSClient++\scripts\updateagent.txt %SystemDrive%\NSClient++\install\updateagent.txt
at %1 "%SystemDrive%\NSClient++\install\updatecmd.bat"
goto exit_0
:exit_usage
ECHO ERROR: You didn't provide time.
ECHO Ex: ./check_nrpe ... -c UpdateAgent -a 03:30PM
:exit_0

NSC.ini file (NRPE custom command)

command[UpdateAgent]=scripts\update.bat $ARG1$

If you have any doubts about this solution please don't hesitate and contact me:

contact at djmario dot ro

Thank you. marius chisa