Did you confirm the database settings on the Setup Manager page? You need to disable flat-file and enable mySQL. Also, make sure that you imported the events into the correct database. The table is normally named epc_calendar unless it was changed in the config file, but the database name is set in the Setup Manager.
Also, which version of the calendar do you have? If it's an older version, it's possible the table format changed. Importing has been tested on 6.3.24 only as that's been the stable release for the past year already.
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