The following error occured: ... nothing..?

I'm trying to figure out a problem jsfl seems to be having (in actionscript), but it won't say what the problem is. I've narrowed the problematic code down to the following:

Code:

---

var fillObj:String = "fl.getDocumentDOM().getCustomStroke(\"toolbar\").shapeFill"

//error occurs past this point:
var nullOrNot:String = MMExecute(fillObj + " == null")
if (nullOrNot == "true")
{
        return
}

---

When this runs and nullOrNot evaluates to "false", the if statement is skipped (the function continues as it should instead of hitting the return), but I get the following output:

The following JavaScript error(s) occurred:

And that's it. Any ideas?
Thanks,
Mavrisa

Moved to Javascript.