Looks like premium.

I'm really no SQL expert but I found this is the Knowledgebase.   About all it says unfortunately is this is the problem but not how to fix it.  Might mean something more to the people who are more versed in SQL than I.

Error: Error Exeucting SQL for table xxxx: Violation of PRIMARY KEY constraint xxxx Cannot insert duplicate key value

This happens when the SQL_Identity is out of snce next Id number

ID:68560Last Modified Date:8-5-2016  

This looks like what I need, but the post does not include any steps. It just describes the issue. 

What version of Sage 100 Premium are you on? Do you have a custom trigger on AR_Customer table that runs on For Insert or For Update? That was the case last time I saw this error. The actual error was in the T-SQL of the trigger but it showed up as "Cannot insert duplicate key" in Sage.

SQL Collation method set correctly?

Any invisible characters (CRLF) in the key fields?

That Knowledgebase article is referring to CRM and the CRM Database. 

The SQL_Identity table exists in CRM database. 

If the issue was creating a new company in CRM and you were getting duplicate key error, you can check the ID_NEXTID value for ID_Tableid = 5 in CRM's SQL_Identity table and then compare to the highest Comp_CompanyID value on the Company table in CRM database to make sure they match.

This would not apply to the Sage 100 Premium database MAS_zzz (company code) and the AR_Customer table getting error, though.

I would check the SQL logs in SQL for other errors.  And also check that the owner on all the Sage 100 Premium databases is MAS_USER (this can change if database restore was done).