Outlook crashes with error message "Only one version of Outlook can run at a time"

Check if multiple process of Outlook.exe is running in the task manager.
· Press Ctrl+Alt+Del, and then chose Task Manager.
· Under processes tab look for Outlook.
· If you find the Outlook process running, right click on it and end the process.
If you do not see multiple process running in the background, then try opening Outlook in safe mode and check the result:
·         Hold Windows key + R.
·         Copy and paste, or type the following command in the Open box, and then press Enter:
Outlook /safe
Note: There is space between Outlook and /.