Cisco VPN :: ASA 5510 / Vpn Goes Down Intermittently For One Or More Locations

We are facing a major issue of VPN tunnel going down very often. I have 7 Site-2-Site VPN connectivity, this works fine for some days and suddently VPN tunnel goes down intermettenly for one or few locations and i need to clear isakmp sa for that speicific tunnel to come up.When tunnel goes down the vpn phase 1 status.....
  
6   IKE Peer: 125.18.0.38
    Type    : L2L             Role    : initiator
    Rekey   : yes             State   : MM_ACTIVE_REKEY
7   IKE Peer: 125.18.0.38
    Type    : L2L             Role    : responder
    Rekey   : no              State   : MM_REKEY_DONE_H2
  
After clearing phase 1 for specific tunnel the VPN tunnel come up.
 
7   IKE Peer: 125.18.0.38    Type    : L2L             Role    : responder    Rekey   : no              State   : MM_ACTIVE
 CINBLR01-SQDR-FIREWALL-00002# sh version
 Cisco Adaptive Security Appliance Software Version 8.0(4)Device Manager Version 6.1(5)
 Compiled on Thu 07-Aug-08 20:53 by buildersSystem image file is "disk0:/asa804-k8.bin"Config file at boot was "startup-config"
 CINBLR01-SQDR-FIREWALL-00002 up 1 day 17 hours
 Hardware:   ASA5510-K8, 256 MB RAM, CPU Pentium 4 Celeron 1600 MHzInternal ATA Compact Flash, 256MBBIOS Flash M50FW080 @ 0xffe00000, 1024KB

[code]....

This platform has an ASA 5510 Security Plus license.