I don't think you can shut anything off, accidently or otherwise. Have you
checked your Junk email folder? If at work, ask the email administrator if
they are filtering meeting requests. Some sites have a problem with meeting
request spam and may be blocking them. (Our Nigerian friends discovered they
have a slightly better chance people seeing their plea for help in getting
their uncle's millions out of the country if they send it as a meeting
request - it gets processed automatically and added to calendars - then pops
up a reminder later. )