Cisco WAN :: 7200 / 2921 With VTI IPsec

We have a Cisco 7204 G1 running c7200-advipservicesk9-mz.122-33.SRE7.bin and we're having a lot of difficulties getting a VTI working to a Cisco 2921 with adv. security. I've ruled out that the 2921 is at fault by successfully establishing a VTI to another 2921 and a 7200 running a different IOS release.
 
We see the tunnel come up, but when I sent a ping from the 2921 to the 7204 there isn't a reply. When I look at the results on the 7204 from a 'sh crypto engine connection active', I see the decrypt counters increase, but I don't see the Encrypt counters increase as it's trying to reply to the ping.  I'm not sure if this is because there is an issue with the encryption or whether there might be a more fundamental issue with the router not replying to the pings.
 
I've tried the following IOS releases (c7200-advipservicesk9-mz.122-33.SRE7 & c7200-advipservicesk9-mz.122-33.SRE6) and they all behave the same way - this makes me think it might be a config issue rather than and IOS bug which is what I first thought. c7200-advipservicesk9-mz.122-33.SRE7.bin.  
 
sh crypto engine connections active
Crypto Engine Connections 

   ID Interface       Type  Algorithm           Encrypt  Decrypt IP Address
    1 Tu10             IPsec 3DES+SHA                 0       31 10.5.5.1
    2 Tu10             IPsec 3DES+SHA                19         0 10.5.5.1
1001 Tu10           IKE   SHA+3DES                  0        0 10.5.5.1
 
Here is a copy of my config on the 7204 - the other end (Cisco 2921) is configured in the same way.
 
crypto isakmp policy 1
encr 3des
authentication pre-share
[code].....