I am having this same issue. If you try and bulk edit user to approve them all you get an error page from wordpress that reads:
“Are you sure you want to do this?
Please try again.”
I see that you sushmitha had this problem about a month ago, but the developer never responded. Does anyone know if he still currently supports the plugin he wrote?
I read in some posts that this error message is usually associated with a security issue. I disabled everything that had would hinder cookies from being loaded.