Conversion of unit of measure & to & in pool & & not possible

What causes this issue?

The unit of measure conversion was not successful.

How to fix this error?

Check whether the entries in table T006 and the alternative unit in the
material master record have been maintained correctly.
If you cannot locate the error, revise your pool allocation and check
that the units of measure for the individual materials can be converted
into the pool unit (table TPOOL).

Error message extract from SAP system. Copyright SAP SE.