Recently, while I was scheduling a live meeting for one of my online training sessions, I kept receiving the following error message repeatedly. I had never encountered this type of error before, and despite searching online for a long time, I could not solve this problem.
After several failed attempts, I finally managed to fix this error with the help of Solid Quality Mentors IT Support Mentor – Victor. He suggested that instead of just typing my name in the “To” field, I should clear the cache by pressing CTRL + DELETE or perform force lookup by selecting the contact person from the global directory.
First click on the “To” field in your new email window in MS Outlook and lookup the person’s email from the global directory, as showed in image below.
Now, try to send the email; you will be able to send the invitation successfully!
Reference: Pinal Dave (http://blog.SQLAuthority.com)