CATIA钣金制作的时候出现错误。

CATIA钣金制作的时候出现错误，请高手给解释一下。
you are trying to create a sheetmetal part in the sheetmetal design workbench.
sheetmetal parts can only be created in the generative sheetmetal design workbench.
please select generative sheetmetal design workbench to create your new part.