Immediate Payment:
While you're out of the office, someone contacted one of your employees with access to your bank account and provide him/her with documentation from you, instructing them to make a transfer payment on your behalf right away so that you can close a crucial deal. By the time you return and discover the problem, it's too late. The scammer took the money and ran.
 

Protect your business: 
Put procedures in place to prevent payments without your direct knowledgement and involvement. If other employees have access to your business bank account, it should be for making specific payments to known vendors. There should be ways to check to ensure that you're making payment to those known vendors. Sudden and surprise request for payment should receive lots of scrutiny.