Exchange Cluster Failover after all IIS

We are using Exchange 2k on Win2k Cluster. For quite some time our exchange resources do not remain on Node 1 for more than 3-4 hrs.& always move to Node 2 with all IIS related services like pop3, imap4, http, smtp failing. We get event id 2074 on application log & 1069 in system log. We have not done any changes.