Why I receive error even follow step by step from matlab documentation in order to open multiple files

Hi.

I have 822 datafile in .dat file and need to process data from row 6886,6886 only. I have follow step by step from the link:

http://www.mathworks.com/help/matlab/import_export/import-data-interactively.html#btiwjhv

but got error:

Error using textscan Invalid file identifier. Use fopen to generate a valid file identifier.

Error in output (line 29) dataArray = textscan(fileID, formatSpec, endRow-startRow+1, 'Delimiter', '', 'WhiteSpace', '', 'HeaderLines', startRow-1, 'ReturnOnError', false);

What is the mean of the error what cause it? Thank you