I had the plugin working but it only allowed me to crop the thumbnail size and a custom size called detail. I wanted to change the medium and large sizes, so I tried uninstalling and deleting, then reinstalling. After reinstalling I cannot use the plugin at all, I get the errors seen by others here.
When going to the settings page I get:
Fatal error: Cannot use string offset as an array in /home/asha/public_html/ma/wp-content/plugins/manual-image-crop/lib/ManualImageCropSettingsPage.php on line 151
When trying to crop an image, no sizes come up and I get the error:
Fatal error: Cannot use string offset as an array in /home/asha/public_html/ma/wp-content/plugins/manual-image-crop/lib/ManualImageCropEditorWindow.php on line 53
I have no other media plugins, I use the standard wordpress to resize - no timthumb or anything. My website is still in testing but can be found at http://mythicalarchive.com/ma/
I hope this helps you isolate the issue.