This type of database corruption is the result of a problem encountered when the database server attempts to search the linked list of the database for the specific table or record and the table or record is not present on the page found in the linked list. This can also indicate a problem with the database linked list, or pages missing from the database linked list.

The ideal situation for recovery from any type of database corruption is to use a tested backup and recovery strategy. A tested backup and recovery strategy ensures that there is no loss of data from database corruption.

If there is no tested backup and recovery strategy, or if it is discovered that the backups are corrupt, there is a method that may allow you to salvage data from the corrupt pages. Depending on the number of pages corrupted, this type of corruption can be isolated to a single table, or spread over spanning multiple tables. With data salvage, there is never a guarantee as to the amount of data that can be salvaged or the integrity of the data that is salvaged.

Unload utility provides the ability to automatically rebuild a database using either the -ar, -an, or -ac options.

If the above procedure does not work to resolve the database assertion error, then it is recommended connect with Technical Support team.

Read this article for more details: Salvaging Data When There are Corrupt Pages in the Database

You can also try 3rd party repairing software like SQL Anywhere repair software from Stellar Phoenix