Handling unit type & is not compatible with current block definition

What causes this issue?

The handling unit type (HU type) of the first handling unit to be put
away determines how many HUs can be put away in one storage bin. If a a
HU with a different storage unit type is put away in this storage bin
and the <ZK>maximum number of handling units per block</> is the same as
the first HU, then the system allows this.
In this case, the storage unit type of the HU to be put away is not the
same as the HU type of the existing HU. Therefore, the definition of the
maximum number of HUs per block is different.

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?

Put this HU away in a different storage bin.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.