Improper RAC Load Balancing

Oracle 9.2.0.8 on Windows 2003 Server.  We are experiencing problems with the database connectivity from the production web servers for the last 2-3 weeks. We are using Oracle RAC and there are 2 database servers. The load seems to shift until most of the connections are going to the same Oracle node i.e. second node. We are using Windows load balancing and all microsoft drivers on the web servers. Does anybody have any idea what might cause this?

LISTENERS_xPC =
  (ADDRESS_LIST =
    (ADDRESS = (PROTOCOL = TCP)(HOST = XXX.XXX.XX.XX)(PORT = 1521))
    (ADDRESS = (PROTOCOL = TCP)(HOST = XXX.XXX.XX.XX)(PORT = 1521))
  )
 
LISTENER_xPC1 =
  (ADDRESS = (PROTOCOL = TCP)(HOST = XXX.XXX.XX.XX)(PORT = 1521))
 
LISTENER_xPC2 =
  (ADDRESS = (PROTOCOL = TCP)(HOST = XXX.XXX.XX.XX)(PORT = 1521))
 

xPC =
  (DESCRIPTION =
    (LOAD_BALANCE = on)
    (FAILOVER = on)
    (ADDRESS_LIST =
     (ADDRESS = (PROTOCOL = tcp)(HOST = XXX.XXX.XX.XX)(PORT = 1521))
     (ADDRESS = (PROTOCOL = tcp)(HOST = XXX.XXX.XX.XX)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = PC)
      (FAILOVER_MODE =
        (TYPE = session)
        (METHOD = basic)
      )
    )
  )
 
PC1 =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = XXX.XXX.XX.XX)(PORT = 1521))
    (CONNECT_DATA =
      (SERVICE_NAME = pc)
      (INSTANCE_NAME = pc1)
      (SERVER=DEDICATED)
    )
  )
 
PC2 =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = XXX.XXX.XX.XX)(PORT = 1521))
    (CONNECT_DATA =
      (SERVICE_NAME = pc)
      (INSTANCE_NAME = pc2)
    )
  )