Thanks for the idea. I'm afraid your regex didn't work but the problem was, indeed, the spaces. I rewrote the expression as

$errmsg =~ /^         # start at beginning of string
             (?:      # look at first group
              \[      # an opening square bracket
              [\w ]+  # followed by one or more word char/spaces
              ]       # followed by a closing square bracket
             )        # end first group
              {3}     # capture should be 1 time 
             (        # begin second capture
              .+      # match anything else 1 or more times
             )        # close second capture
[download]

and it works as needed. Thanks again