Problem of VPN client to site on SSG 5

Hello all,

I have configured VPN client to site on SSG5 recently. also, I configured profile on client as well,the client use NCP Secure Entry Client as VPN client software to connect remotely,  the clients can connect successfully  VPN through internet 3G sim card but not successfully through WIFI connection although WIFI connection always in good condition. The client showed error "VPN error Connection to VPN gateway failed". as on NCP client software.
I cannot find how is reason. someone suggest me.

Thank in advance.