same issue occur again, can you help me on that ? thanks

Hello Sir,

We have checked and found that since yours is a free account, it has limited space which was exceeded as uKnowva keeps writing system logs, etc, hence you were unable to export any file from the system. I have temporarily fixed this problem, but this will surely come again in future again. We request you to please upgrade to a paid subscription to get more disk space. Moreover you get personalized support as well. Please connect with our sales team for more details on this.

Regards,
Amit Aher

Thanks for that! sure.