No buffer space available (maximum connections reached?)

Yesterday a portal cluster stops to respond requests after 4 months of work without a restart.

I found a lot of messages on systemout.log

8/25/14 10:13:21:418 BRT] 00000171 exception     E com.ibm.ws.wim.adapter.ldap.LdapConnection DirContext reCreateDirContext(String errorMessage)
                                 com.ibm.websphere.wim.exception.WIMSystemException: CWWIM4520E  'javax.naming.CommunicationException:  [Root exception is java.net.SocketException: No buffer space available (maximum connections reached?): connect]'

This Microsoft TechNote explain the problem with Windows 2008 R2