Materials is available in the material list more than once

What causes this issue?

One material exists several times in the material list. You have
assigned this material to the same operation or phase more than once.

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?

Check the material assignments at the operations and phases.
Check whether you can combine the material into one item in the bill of
material (BOM).

Procedure for System Administrators

&HINT&
In Customizing, you can define how the system is to treat this system
message. To do so, go to Customizing for <LS>Production Planning -
Process Industries</> and choose <LS>Master Data</> -> <LS>Master
Recipe</> -> <LS>Settings for the Task List Type</> -> <LS>Determine
System Message Features</>.
Note that this message is displayed only if you have set the type <LS>W
</> (warning). With all other message types, the message is not
displayed.

Error message extract from SAP system. Copyright SAP SE.