Bootstrap

Dear All,

I would like to use the bootsrap estimation but STATA displays the following error:

bootstrap _b: xtgls ccp qa1 trans1 iqae taille lev roa age, panels (hetero) corr (ar1)
(running xtgls on estimation sample)

Bootstrap replications (50)
----+--- 1 ---+--- 2 ---+--- 3 ---+--- 4 ---+--- 5
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 50
insufficient observations to compute bootstrap standard errors
no results will be saved
r(2000);

I have tried several solutions but the problem is not solved. Can you help me?

Many thanks!