Error Message - Duplicate Entry

I'm running with Sage 50 Premium Accounting 2021.1.1 version.

I haven't been able to create a new inventory ID since last month, and the manager has had a problem from today.

When I go into create a new Stock ID, show up this message: "You have entered a value that has been assigned to another record. You cannot have two records with the same value.".

We tried to solve the problem through the link below, but all failed.

https://support.na.sage.com/selfservice/viewContent.do?externalId=15720&sliceId=1

Please help if anyone could give advise or instructions.