Have you included Ace Timer when you defined your addon? You also need to include the library using your .toc or embeds.xml.
Code:
MyAddon= LibStub("AceAddon-3.0"):NewAddon("MyAddon", "AceTimer-3.0")
Another thing to note is that you dont prefix methodToRun with your addon name i.e. dont do this
MyAddon:ScheduleRepeatingEvent("MyAddon:methodToRun", 0.2)
Do this, note the quote marks
Code:
MyAddon:ScheduleRepeatingEvent("methodToRun", 0.2)