My browser tried to open a >100M .log file from the net instead of download.
I searched another solution:

cURL is useful console program. You can use it on Windows also : http://curl.haxx.se/download.html
C:WindowsSystem32>curl http://servername.com/path_to_logs_file/portal_error-20140717.log > E:testfolderportal_error.log
% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
Dload  Upload   Total   Spent    Left  Speed
100  176M  100  176M    0     0  1826k      0  0:01:38  0:01:38 –:–:– 1900k