在使用xttobit命令时候出现下列问题

. xttobit lev1 growth2 age2 liq risk mortgage roa ntds size unique

Obtaining starting values for full model:

Iteration 0:   log likelihood = -26855.346

Iteration 1:   log likelihood = -26794.826

Iteration 2:   log likelihood = -26794.303

Iteration 3:   log likelihood = -26794.302

Fitting full model:no room to add more variables because of width

An attempt was made to add a variable that would have increased the memory required to store an observation beyond what is currently possible.

请问这个是怎么回事儿 是不是变量有什么要求

还是我的命令不正确 如果是应该注意什么问题？？？？？