Cisco VPN :: 1841 / 1801 - Random L2L IPSEC VPN Disconnect

Network Setup
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2 Site to Site VPN tunnels has been established, it is a hub and spoke topology. The hub is ASA5520 and the 2 spoke are a 1841 and 1801 router. The tunnel is able to pass traffic, it's a full tunnel VPN.The tunnel randomly disconnect for no reason. When I check the logs I can see some errors :

%CRYPTO-4-RECVD_PKT_INV_SPI: decaps: rec'd IPSEC packet has invalid spi for destaddr=x.x.x.x, prot=50, spi=0x5F822579(1602364793), srcaddr=y.y.y.y
%CRYPTO-4-IKMP_NO_SA: IKE message from y.y.y.y has no SA and is not an initialization offer
 
The actual address have been replace by x.x.x.x and y.y.y.y. I frequently have to peform clear crypto isakmp on the spoke routers to revive the VPN tunnels. Is there a way the tunnel can be re-establish again without manual intervention?This keep happening on a random basis and I have living with it for years. I have looked at cisco website troubleshooting tips and but no luck in finding out how to resolve it.
 
Below is my config on one of the spoke router:
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Cisco IOS Software, C180X Software (C180X-ADVIPSERVICESK9-M), Version 12.4(24)T3, RELEASE SOFTWARE (fc2)
crypto isakmp policy 10encr 3deshash md5authentication pre-sharegroup 2crypto isakmp key @@@@@@ address y.y.y.ycrypto isakmp invalid-spi-recoverycrypto isakmp keepalive 30 periodiccrypto isakmp nat keepalive 20!!crypto ipsec transform-set tset1 esp-3des esp-md5-hmaccrypto ipsec df-bit clear!crypto map ipsecvpn 10 ipsec-isakmp
set peer y.y.y.yset transform-set tset1match address vpn@spoke!archivelog config  hidekeys!!!!!interface FastEthernet0ip address x.x.x.x 255.255.255.248ip nat outsideip virtual-reassemblyduplex autospeed autocrypto map ipsecvpn!interface FastEthernet1!interface FastEthernet2!interface FastEthernet3!interface FastEthernet4!interface FastEthernet5!interface

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