Seaquel
SQL Server error code

SQL Server error 5323

SQL Server raises error 5323 at severity 15, which marks a problem with the query or data that you can correct.

Subqueries are not allowed in the %S_MSG clause when the FROM clause contains a nested INSERT, UPDATE, DELETE, or MERGE statement.
Msg5323
Severity15
Group5000–5999

Source: Database Engine events and errors