Error in the alert log

We recently created 11g database and imported data from 9i. Today I see the following errors in the alert log.

Fatal NI connect error 12170.

  VERSION INFORMATION:
 TNS for 64-bit Windows: Version 11.2.0.1.0 - Production
 Oracle Bequeath NT Protocol Adapter for 64-bit Windows: Version 11.2.0.1.0 - Production
 Windows NT TCP/IP NT Protocol Adapter for 64-bit Windows: Version 11.2.0.1.0 - Production
  Time: 05-SEP-2011 11:52:08
  Tracing not turned on.
  Tns error struct:
    ns main err code: 12535
   
TNS-12535: TNS:operation timed out
    ns secondary err code: 12606
    nt main err code: 0
    nt secondary err code: 0
    nt OS err code: 0
  Client address: (ADDRESS=(PROTOCOL=tcp)(HOST=xxx.xx.xx.xx)(PORT=11111))