Thumbnails not showing

Hi everyone,
I'm setting up Omeka and Scripto at itranscribe.com.au for Queensland State Archives. But I can't get thumbnails to show. When I enable the GD file derivative strategy the thumbnails don't show. ImageMagick isn't installed on the hosted shared server, so I can't use that, and I don't have SSH access. And when I try the Imagick file derivative strategy I get the error below. Does anyone know how I might be able to solve this?

Omeka_File_Derivative_Exception
This derivative strategy requires ext/imagick.

exception 'Omeka_File_Derivative_Exception' with message 'This derivative strategy requires ext/imagick.' in /home/itit6435/public_html/omeka/application/libraries/Omeka/File/Derivative/Strategy/Imagick.php:27
Stack trace:
#0 /home/itit6435/public_html/omeka/application/libraries/Omeka/Application/Resource/Filederivatives.php(43): Omeka_File_Derivative_Strategy_Imagick->__construct()
#1 /home/itit6435/public_html/omeka/application/libraries/Zend/Application/Bootstrap/BootstrapAbstract.php(695): Omeka_Application_Resource_Filederivatives->init()
#2 /home/itit6435/public_html/omeka/application/libraries/Zend/Application/Bootstrap/BootstrapAbstract.php(638): Zend_Application_Bootstrap_BootstrapAbstract->_executeResource('filederivatives')
#3 /home/itit6435/public_html/omeka/application/libraries/Zend/Application/Bootstrap/BootstrapAbstract.php(598): Zend_Application_Bootstrap_BootstrapAbstract->_bootstrap(NULL)
#4 /home/itit6435/public_html/omeka/application/libraries/Zend/Application.php(371): Zend_Application_Bootstrap_BootstrapAbstract->bootstrap(NULL)
#5 /home/itit6435/public_html/omeka/application/libraries/Omeka/Application.php(51): Zend_Application->bootstrap()
#6 /home/itit6435/public_html/omeka/index.php(23): Omeka_Application->initialize()
#7 {main}

If imagemagick isn't installed, then IMagick won't work either, so GD is still likely the best way to go. It might just be that GD doesn't know what to do with the files. What file type(s) are they, and does it fail for all file types?