The tech note describing using eval on the left side of an operator has been updated to take note of an issue that has arisen.
eval("TextField" + "One") = "string1″ trace("TextFieldOne")
Will return “undefined” in Test Movie and the eval() will fail in Macromedia Flash Player 6.
To correct the problem enclose the string concatenation in an extra set of parentheses:
eval(("TextField" + "One")) = "string1″;
You can find more info on eval in this post.