regardless of where the data is (field 1 or field 2).

The key must be either in field 1 or in field 2. It can't vary by row. You're providing

                   Field 1      Field 2      Field 3
                   -----------  -----------  -----------
  56 1752.eps      "",          "56",        "1752.eps"   key in 2
1160 trace.exe     "1160",      "trace.exe"               key in 1
 123 foo bar.pl    "123",       "foo",       "bar.pl"     key in 1
[download]

You need to normalize your fields so that they are the same for each row. I did it by removing the extraneous delimiter in the front of some lines.

                   Field 1      Field 2      Field 3
                   -----------  -----------  -----------
56 1752.eps        "56",        "1752.eps"                key in 1
1160 trace.exe     "1160",      "trace.exe"               key in 1
123 foo bar.pl     "123",       "foo",       "bar.pl"     key in 1
[download]

You could also add an extraneous delimiter to the lines that don't have one.

                   Field 1      Field 2      Field 3      Field 4
                   -----------  -----------  -----------  -----------
   56 1752.eps     "",          "56",        "1752.eps"
 1160 trace.exe    "",          "1160",      "trace.exe"
  123 foo bar.pl   "",          "123",       "foo",       "bar.pl"
[download]

By the way, why not just let ls do the sorting if you're going to use ls?

Update: Improved visuals.