Command not supported.

I'm a beginner to stm32 world, and currently using STM32F407VG and the KEIL version is MDK 5.30. I started with the basic example blinky code. And when I'm trying to flash the code a dialogue box is popping with a message "Command not supported" and "Error: Flash Download failed  -  Target DLL has been cancelled" followed by it. It will be very helpful if I got a solution for this.

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