Error: Shipping method required!

hello all

I am getting lots of eerror messages when a customer selects a shipping method. They select the shipping method and click "Continue" - the method exists and the customer selects it properly but some users get the following error message:

Error: Shipping method required!

The vendor of the mod has researched the issue and believes it is caused by the session data's "shipping_methods" array being unset or cleared.

In addition, we are getting some orders coming through without the shipping method set in the db so the order doesn't have a shipping details tab in the admin order details screen.

Any tips on this error?

Thanks!!!

Simon