i ran into the same issue where i needed to send a message to remote computers over the network and net send is not an option. I created this small simple script that will do it without any registry tweeks. you just need suficient privilages.
copy text below and paste in notepad. then save it as .bat
@ECHO OFF
color 74
REM - Created by Joe Kazlauskas
REM - 2OCT2013
REM - Send a Message.
ECHO.
:1
ECHO.
set /p NAME= ENTER Remote Computer Name or IP address:
set /p MESSAGE= Type your message here:
wmic /node:%NAME% process call create "msg * /w %MESSAGE%"
ECHO.
set /p ANOTHER=Do you want to send another message: y/n?
IF %ANOTHER%==y GOTO :1
IF %ANOTHER%==n GOTO :2
ECHO.
:2
pause