Hi,
From the error description, the problem seems to be with editing schemas in Adobe Campaign Classic.
When you are creating or editing data schemas, if you happen to make mistake in schema definitions, until the problematic schema is corrected, you keep getting these kind of errors for all new schema additions or modifications.
So, from update database structure, identify the data schemas in which there is structural mismatch between UI and DB.
Navigate to the identified schemas and try to figure out and fix the problematic data schema with invalid schema definitions or XML structure.
Hope this helps!