To understand this question, the user needs to know what SQL is and its error codes. SQL (Structured Query Language) is a programming language used to manage and manipulate relational databases. SQL error codes are used to indicate any errors or problems that occur during SQL processing.

Option A: Authentication failure. This error occurs when a user provides incorrect login credentials while trying to access the database. However, SQL code -818 is not related to authentication failure.

Option B: SELECT statement has resulted in retrieval of more than one row. This error occurs when a SELECT statement is expected to return only one row, but it returns more than one row. However, SQL code -818 is not related to this error.

Option C: Generated when the consistency tokens in the DBRM and the load module are different. This error occurs when there is a mismatch between the consistency tokens in the DBRM (Database Request Module) and the load module. Consistency tokens are used to ensure that the DBRM and the load module are in sync. SQL code -818 is related to this error.

Option D: Resource Unavailable. This error occurs when the required resources are not available in the system. However, SQL code -818 is not related to this error.

Therefore, the correct answer is:

The Answer is: C. Generated when the consistency tokens in the DBRM and the load module are different.