Plugin stops on the first image

Hi,
Used this plugin for a website containing 24 images. Plugin shows massage “Rebuilding 1 of 24”, but doesn’t proceed further. Waited for 15 minutes, no progress. Checked the directory manually, can find the resized file for the first image which is processed. But no other file resized.

https://www.ads-software.com/plugins/ajax-thumbnail-rebuild/