HU WT cannot be confirmed due to open product WTs for HU

What causes this issue?

You want to confirm an HU warehouse task into a storage type where
putting away HUs is not permitted. Here, only the products in the HU are
put away into the storage type.
However, there are still open product warehouse tasks that are to be
removed from stock by this HU. Performing this confirmation would leave
these pointing to nothing.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

First cancel all open product warehouse tasks for the HU.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.