Sql*loader error:unable to open file:Tns Protocol adaptor error!

Hi all!

Query:

1.I am trying to load data from Excel into Oracle Table through Sql*Loader.

First,I converted the datas to be added into Oracle Table into notepad using:
CSV (COMMA DELIMITED) in Excel File.

Then opened the above excel file into Notepad by naming the file as:
LOAD3.CTL being the control file.

As I am performing LOADING WITH EMBEDDED DATA:

My Control file LOAD3.CTL consists of:

LOAD DATA
INFILE *
APPEND
INTO TABLE APPLICANT_MASTER_HEADER
FIELD TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'
(COLUMN1,COLUMN3,COLUMN5,COLUMN10,...)

BEGINDATA

7787,HDFHFG,JDKDFK,
..................
..................

P.S:

1).The above table is not empty but already contains some datas.The above control file
would add more datas to the existing tables into specific table columns as mentioned above.

2).I do want to append to few specific columns only that's why I had added columns with
column1,column3,column5,etc.,

When I run sqlldr,it throws error like:

D:\>sqlldr scott/tiger control=load3.ctl log=load3.log
Oracle Internal Error.OCI error.
TNS protocol adaptor error.

3).Whenever I run sqlldr by saving the data files,control files with sql extension,it executes
successfully.But when I save it with DAT,CTL extension,it says:"UNABLE TO OPEN FILE.

Any idea what could have gone wrong.

What should be done to resolve the above error.

Thanks&Regards,

Amit.