Remote VPN, logged on, but cannot access anything

[rhienwei2010]

I have setup IPsec remote VPN, some time, just some time, when clients didn't use 'Enable Transparent Tunneling',  the clients could logon, passed user validation, got IPs, but could not access anything internal, failed to ping to any internal IPs.  Checked firewall(ASA 5520) logs, it showed the client VPN IP sent packets to internal IPs correctly.  But it just failed to access internal networks.

Any clues?

[rhienwei2010]

'IPsec over UPD' had this issue as well.  'IPsec over TCP' most time were fine after logon, but some time clients cannot connect to my firewall through TCP mode.

Any Cisco Superheros can help?