some broken thumbnails

Hi,
Some of the thumbnails did not work, so i decided to update the plugin. But this changed most the thumbs in the frontend into circles and in the backend still the same problem .
http://www.gbscalvijn.nl/fotos/?file=Bezoek+Koning+en+Koningin%2F&lg_pagei=2 is an example of the frontend.
But in the backend i just see Alert signs on some folders:
http://db.tt/aq0xEbwy
http://www.gbscalvijn.nl/fotos/?file=Bezoek%20juf%20Stieneke/foto%27s%20bezoek%20Stieneke%20005.jpg

It is strange, because sometimes it looks like it is working, but when i ask the client to upload new images it stopped working again.

This mentioned, the problem started since we have changed servers

Kind regards,
NMCI

http://ww.wp.xz.cn/extend/plugins/lazyest-gallery/