This can happen if the Cisco Adaptive Security Appliance (ASA) software is not licensed for the Multiple Context mode.
As a workaround, issue the show version command at the prompt. When the output of the command pops up, check for this line:
Security Contexts : 0 <<<< not licensed
A value of 0 indicates that the ASA is not licensed for the Multiple Context mode.
Refer to Enabling Multiple Context Mode for more details.
In order to apply for a new Multiple Context license, go to email@example.com.