[CentOS] VPN inside VPN?

Hi all,
Just wondering if VPN inside VPN is possible?
I've created PPTP VPN in the office.
Then from home, first I need to use company's official AT&T VPN.
Then after connected, I fire up the PPTP VPN client.
Got connected, but cannot ping the PPTP gateway, and half minute later
the PPTP got disconnected.
No obvious error message in the PPTP log.

Thank you.