Getting a prompt always "A purchase type must be entered.Select shipping from options menu" while su

Hi,

We are getting the prompt saying "A purchase type must be entered.Select shipping from options menu".

And one more problem is that before submitting a PO I can add it and while approving also am getting the same error. But the problem is that while approving am unable to select even the option as it is disabled.

Please have a look at the screen shots and kindly suggest and solution.

Thanks.