You can't have an alias named timer(anything). /timer is a mirc command that is allowed to have text appended to it to give the timer a name. You can also use, for example /timername, to display the status of a timer named "name". That's where the "timer name is not active" message is from.

You need to add a name for your alias along the lines of...
Code:
mytimer timerName 0 30 msg $chan My message goes here.


($chan is valid in aliases called from events as well as from the commandline)