Read the xlsread documentation: On Windows® systems with Microsoft Excel software, xlsread reads any file format recognized by your version of Excel. If your system does not have Excel for Windows, xlsread operates in basic import mode, and reads only XLS, XLSX, XLSM, XLTX, and XLTM files. You write that you are using a Linux server, and the documentation does not list CSV as being a supported format for Linux systems.
Also note that it is better to use fullfile to generate filepaths, rather than by string concatenation: [data_dir filesep instrument filesep...].
In any case there is a much more important question for you: why use xlsread to read a CSV file anyway? Why not use one of the CSV-reading tools, such as csvread ? This would resolve this issue completely.
Important: You need to change the variable name sum, which is used as the input argument to the function parse_VINDTA. sum is an inbuilt function in MATLAB, so shadowing its names is a really bad idea. For the same reason avoid variables names i, j, length, prod, etc.
