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An error occurred creating the configuration section handler for system.data: Column 'InvariantName'
An error occurred creating the configuration section handler for system.data: Column 'InvariantName' is constrained to be unique. Value 'MySql.Data.MySqlClient' is already present. (C:\Windows\Micros...
In my case I upgraded v8.0.30 to v9.0.0 and found a duplicate entry in the machine.config file.
Deleted the line that was related to old version.
Restarted machine.
Everything is working ok now.
Thanks.