Question : ORA-12560: TNS:protocol adapter error

What could be the reason for following error message while connecting to Oracle database server :
ORA-12560: TNS:protocol adapter error

Answer : ORA-12560: TNS:protocol adapter error

>> sqlldr control=C:\XCS\ARLoader\writer\vg3\bcacct.ctl data=C:\XCS\ARLoader\writer\vg3\bcacct.dat

the sqlldr needs the userid parameter - where are you giving that:

This is the usage of sqlldr:

Z:\>sqlldr

SQL*Loader: Release 9.2.0.1.0 - Production on Wed May 9 16:07:24 2007

Copyright (c) 1982, 2002, Oracle Corporation.  All rights reserved.


Usage: SQLLDR keyword=value [,keyword=value,...]

Valid Keywords:

    userid -- ORACLE username/password
   control -- Control file name
       log -- Log file name
       bad -- Bad file name
      data -- Data file name
   discard -- Discard file name
discardmax -- Number of discards to allow          (Default all)
      skip -- Number of logical records to skip    (Default 0)
      load -- Number of logical records to load    (Default all)
    errors -- Number of errors to allow            (Default 50)
      rows -- Number of rows in conventional path bind array or between direct path data saves
               (Default: Conventional path 64, Direct path all)
  bindsize -- Size of conventional path bind array in bytes  (Default 256000)
    silent -- Suppress messages during run (header,feedback,errors,discards,partitions)
    direct -- use direct path                      (Default FALSE)
   parfile -- parameter file: name of file that contains parameter specifications
  parallel -- do parallel load                     (Default FALSE)
      file -- File to allocate extents from
skip_unusable_indexes -- disallow/allow unusable indexes or index partitions  (Default FALSE)
skip_index_maintenance -- do not maintain indexes, mark affected indexes as unusable  (Default FALSE)
  readsize -- Size of Read buffer                  (Default 1048576)
external_table -- use external table for load; NOT_USED, GENERATE_ONLY, EXECUTE  (Default NOT_USED)
columnarrayrows -- Number of rows for direct path column array  (Default 5000)
streamsize -- Size of direct path stream buffer in bytes  (Default 256000)
multithreading -- use multithreading in direct path
 resumable -- enable or disable resumable for current session  (Default FALSE)
resumable_name -- text string to help identify resumable statement
resumable_timeout -- wait time (in seconds) for RESUMABLE  (Default 7200)
date_cache -- size (in entries) of date conversion cache  (Default 1000)

PLEASE NOTE: Command-line parameters may be specified either by
position or by keywords.  An example of the former case is 'sqlldr
scott/tiger foo'; an example of the latter is 'sqlldr control=foo
userid=scott/tiger'.  One may specify parameters by position before
but not after parameters specified by keywords.  For example,
'sqlldr scott/tiger control=foo logfile=log' is allowed, but
'sqlldr scott/tiger control=foo log' is not, even though the
position of the parameter 'log' is correct.