Omeka OHMS Viewer error

Hello-

I have the OHMS Viewer plugin installed in an Omeka instance at https://sandbox.omeka.dpulibrary.org/, and I’m not able to upload any files within Omeka, or even view a file that was uploaded manually into the cachedfiles folder.

here is my config file:
tmpDir = /home/dpulibr/sandbox.omeka.dpulibrary.org/ohms-viewer/cachefiles
players = other,brightcove,kaltura,youtube,soundcloud,vimeo,avalon,aviary
timezone = America/Chicago
exhibit_mode = false
print_mode = false

[DePaul Special Collections and Archives]
css = custom_default.css
footerimg =
footerimgalt =
contactemail = digitalservices@depaul.edu
contactlink =
copyrightholder =
open_graph_description =
open_graph_image =
ga_tracking_id =
ga_host =

and here is the error that displays:

LogicException: OHMS file must be validated before retrieving list of column examples. in /home/dpulibra/sandbox.omeka.dpulibrary.org/plugins/OhmsImport/models/OhmsImport/File.php:62
Stack trace:
#0 /home/dpulibra/sandbox.omeka.dpulibrary.org/plugins/OhmsImport/controllers/IndexController.php(188): OhmsImport_File->getColumnExamples()
#1 /home/dpulibra/sandbox.omeka.dpulibrary.org/application/libraries/Zend/Controller/Action.php(516): OhmsImport_IndexController->indexAction()
#2 /home/dpulibra/sandbox.omeka.dpulibrary.org/application/libraries/Zend/Controller/Dispatcher/Standard.php(308): Zend_Controller_Action->dispatch(‘indexAction’)
#3 /home/dpulibra/sandbox.omeka.dpulibrary.org/application/libraries/Zend/Controller/Front.php(954): Zend_Controller_Dispatcher_Standard->dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http))
#4 /home/dpulibra/sandbox.omeka.dpulibrary.org/application/libraries/Zend/Application/Bootstrap/Bootstrap.php(105): Zend_Controller_Front->dispatch()
#5 /home/dpulibra/sandbox.omeka.dpulibrary.org/application/libraries/Zend/Application.php(384): Zend_Application_Bootstrap_Bootstrap->run()
#6 /home/dpulibra/sandbox.omeka.dpulibrary.org/application/libraries/Omeka/Application.php(73): Zend_Application->run()
#7 /home/dpulibra/sandbox.omeka.dpulibrary.org/admin/index.php(28): Omeka_Application->run()
#8 {main}

Can someone help me figure out what’s misconfigured?