Woocommerce Product CSV Import Suite shows “Access Denied”

I have been trying to upload a simple product with minimum columns in Product CSV Import Suite. But it shows “Access Denied” message after some seconds of starting the import. I am the Super Administrator of the website, but it still shows access denied.
1. I am uploading just one simple product with only 12 columns keeping it minimum.
2. I have tried making another administrator account and trying to import with it, but is still shows the same message.
3. Plugin version is 1.10.38 which I think is the latest.

Is anyone familiar with such kind of behavior?