Don't know why it is not working. As securityk9 is enabled, uou can try another - change the vpdn tunnel to L2TP and try to L2TP to this router and try again. 

Hi,Sorry for the late response. If you are using L2TP, you will need security9k enabled to let L2TP connect to the router. If you are using PPTP, no security9k needed. In ISR family, when you successfully connected to the router via L2TP/PPTP, you wi...

Thanks for your information. Looks like securityk9 is not enabled. I assume you are using L2tp, you need this to be enabled. Try PPTP if you do not want to enable securityk9.

Yes, it works fine. Could you please post show version and show license to see this feature is enabled or not?

Hi,   You'll need to active the feature license called "appxk9" to forward l2tp traffic.   https://www.cisco.com/c/en/us/td/docs/routers/access/4400/software/configuration/guide/isr4400swcfg/bm_isr_4400_sw_config_guide_chapter_0101.html#concept_EE11C...