Active Sync Issue in Exchange 2003

Log --> HTTP/1.1 RPC_OUT_DATA /rpc/rpcproxy.dll?Mail.XYZ.com:6004 - 1 Connection_Dropped DefaultAppPool

We have three Serve two Mailbox Clustered and one frond end CAS for Owa, Oma & ActiveSync.

When we restart the IIS it works but after some 4-5 hrs stops responding for Active Sync only.

Thanks

Vinod