救命啊，总是出现an error occurred when bootstrap executed opreg具体的情况如下的，如果没有加入t这个变量的话，就可以运算出来，但是结果全部都是1的。。。加入了cvars(t) 就会出现
an error occurred when bootstrap executed opreg 。。不知道是为什么，求各位达人解答


. opreglny ,exit(exit) state(lnk)proxy(lni)free(lnl)
(running opreg on estimation sample)

Bootstrap replications (50)
----+--- 1 ---+--- 2 ---+--- 3 ---+--- 4 ---+--- 5
.................................................. 50


Olley-Pakes productivity estimator Number of obs = 816
Group variable (i): id Number of groups = 204
Time variable (t): year
Obs per group: min = 4
avg = 4.0
max = 4

(Replications based on 204 clusters in id)
------------------------------------------------------------------------------
| Observed Bootstrap Normal-based
| Coef. Std. Err. z P>|z| [95% Conf. Interval]
-------------+----------------------------------------------------------------
lny |
lnk | .3610104 .0706505 5.11 0.000 .2225378 .4994829
lnl | .3271804 .0342377 9.56 0.000 .2600757 .394285
------------------------------------------------------------------------------
State: lnk
Free: lnl
Control:
Proxy: lni

. est store OP_all

. opreglny ,exit(exit) state(lnk)proxy(lni)free(lnl)cvars(t)
(running opreg on estimation sample)
t:may not use time-series operators on string variables
an error occurred when bootstrap executed opreg
r(109);

. destring t ,replace
t has all characters numeric; replaced as byte

. opreglny ,exit(exit) state(lnk)proxy(lni)free(lnl)cvars(t)
(running opreg on estimation sample)
an error occurred when bootstrap executed opreg
r(2000);

. destring age ,replace
age has all characters numeric; replaced as byte

. opreglny ,exit(exit) state(lnk age)proxy(lni)free(lnl)cvars(t)
(running opreg on estimation sample)
an error occurred when bootstrap executed opreg
r(2000);

. opreglny ,exit(exit) state(lnk age)proxy(lni)free(lnl)cvars(t)vce(bootstrap, seed(1357) rep(5))
(running opreg on estimation sample)
an error occurred when bootstrap executed opreg
r(2000);

. drop _est_OP_all

. opreglny ,exit(exit) state(lnk age)proxy(lni)free(lnl)cvars(t)vce(bootstrap, seed(1357) rep(5))
(running opreg on estimation sample)
an error occurred when bootstrap executed opreg
r(2000);

. rename lni invest

. opreglny ,exit(exit) state(lnk age)proxy(invest)free(lnl)cvars(t)vce(bootstrap, seed(1357) rep(5))
(running opreg on estimation sample)
an error occurred when bootstrap executed opreg
r(2000);

.

文章后附有原始的文件，求论坛的高手们解答！！
文件位置在：https://bbs.pinggu.org/z_liuliang.php?aid=1152560