We need more infos what you did!

Did you manually try to set a breakpoint? Maybe in a BEGIN-block?

If not, do you have any debugger code in your script?

Try grepping for things starting with "DB::"

UPDATE

Not every source line results in an atomic step at run-time where you can set a breakpoint.

e.g.

• Many lines are grouped together into one step.
• They were only relevant at compile-time.
• Were NOPs (no-operations) like empty lines or comments
• ...

See the following snippet from "Programming Perl" for examples:

To look at a "window" of source code around the breakpoint, use the w command:

    DB<2> w
    5     }
    6
    7       sub infested {
    8==>b       my $bugs = int rand(3);
    9:          our $Master;
    10:         contaminate($Master);
    11:         warn "needs wash"
    12              if $Master && $Master->isa("Human");
    13
    14:         print "got $bugs\n";

    DB<2>
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As you see by the ==> marker, your current line is line 8, and by the b there, you know it has a breakpoint on it. If you had set an action, there also would also have been an a there. The line numbers with colons are breakable; the rest are not.