can't read data files using php inside MAMP

I developed an online store catalog using PHP & MYSQL on Windows.
It imports tab delimited data for new products from text files in a folder.
While it worked fine on Wndows, when I run it in the MAMP installation on my iMac with Mac OSX it is not working. The site itself works, just not the importing part. I'm not getting any sort of error either, so I don't know what's going on.
Here is the relevant code in PHP:

$data = fopen("data/import_products.txt", "rb");  
while (!feof($data)){      
    $thisline = fgets($data);
    echo $thisline;
    $v = explode("\t",$thisline);

here it inserts the data into the database