Are you putting a breakpoint on something that isn't code, like a empty line, a brace, etc? Try altering that to be on a line that has code on it. (I know we should be able to set breakpoints anywhere, but I'm curious).
e.g.
for (var i:int = 0; i < 100; i++) // set a breakpoint here
{ // do not set a breakpoint here
// do not set a breakpoint here
trace(i); // set a breakpoint here
} // do not set a breakpoint here
I'm wondering if it considers empty lines, braces and other things to be invalid for a breakpoint location.
