我在stata上利用findit命令，下载安装了xtabond2。在运行help文档中的例子——Examples

    . use http://www.stata-press.com/data/r7/abdata.dta
    . xtabond2 n l.n l(0/1).(w k) yr1980-yr1984, gmm(l.n w k) iv(yr1980-yr1984, passthru) noleveleq
        small
    . xtabond2 n l.n l(0/1).(w k) yr1980-yr1984, gmm(l.n w k) iv(yr1980-yr1984, mz) robust twostep
        small h(2)
     时出现如下错误

     xtabond2_mata():  3499  strtoreal() not found
                 <istmt>:     -  function returned error
r(3499);
请问这是为什么？如何纠正？

望高手解答，不胜感激