why cannot the generate function be used twice

[WyGongya]

When i invoke the generate function twice with different idx,it appears the fault described as "RuntimeError: The expanded size of the tensor (181) must match the existing size (168) at non-singleton dimension 3. Target sizes: [1, 32, 68, 181]. Tensor sizes: [1, 1, 68, 168]"

should i reset the model' arguements or reload the model?