Question:
When the ASA is configured for multiple security contexts it is not possibel to enable VPN. Why this happens and how can we solve this issue?
Answer:
It is by default that the VPN cannot be confgured on ASA when multiple security contexts are already configured.
Refer to Information About Security Contexts for more information.
Source: https://supportforums.cisco.com/thread/2140570?tstart=0