If your system was upgraded from a version older than R/3 Enterprise, the database owner should be "dbo". In such case, make sure that system profiles match the correct database owner.
Also, check if any system environment variables are set. Their value might be incorrect. Take a look at this link for more information: https://searchsap.techtarget.com/feature/Scenario-2-Dispatcher-dies-due-to-a-database-connection-problem.
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