Originally Posted by rockcavera
I tested the previous versions, the error starts in version 7.53. That is, version 7.52 was the last one that the command worked on.


rockavera: Indeed. That's the version where all the messaging commands had a major overhaul and unification internally.

Code
29/11/2018 - mIRC v7.53
20.Added /privmsg command.
21.Added support for CPRIVMSG and CNOTICE. If listed in numeric 005,
   PRIVMSG and NOTICE will be automatically upgraded for most
   outgoing messages if you are an op/voice on a channel and message
   a user on the same channel.
22.Added support for numeric 005 STATUSMSG=@+ and WALLVOICES and added
  commands /vmsg, /vnotice, and /wallvoices. If server does not support
  STATUSMSG, WALLCHOPS, or WALLVOICES, mIRC uses own method to send to
  multiple targets.
23.Changed line splitting method for long messages when:
   1) Sending message through editbox of a channel/query window.
   2) Using commands /ame /amsg /describe /me /msg /omsg /privmsg /qme
   /qmsg /query /sound /vmsg /wallchops.

   Note: when line splitting, the /sound command switches to an ACTION
   message for the second line onwards.

   Note: line splitting is not performed on NOTICEs, so is not applied
   to /notice /onotice /vnotice /wallvoices.

24.Changed multiple target handling in PRIVMSG and NOTICE so that if
   TARGMAX or MAXTARGETS are not specified in numeric 005, mIRC assumes
   the maximum is one target per message.