OIDplus Error

ViaThinkSoft\OIDplus\OIDplusPagePublicResources::getFolderTitle(): Argument #1 ($dir) must be of type string, null given, called in /daten/homes/oidplus/hosts/hosted.oidplus.com/public_html/viathinksoft_demo/plugins/viathinksoft/publicPages/500_resources/OIDplusPagePublicResources.class.php on line 291

Technical information about the problem:

TypeError
at file .../plugins/viathinksoft/publicPages/500_resources/OIDplusPagePublicResources.class.php (line 698)

Stacktrace:
#0 .../plugins/viathinksoft/publicPages/500_resources/OIDplusPagePublicResources.class.php(291): ViaThinkSoft\OIDplus\OIDplusPagePublicResources::getFolderTitle()
#1 .../includes/classes/OIDplusGui.class.php(42): ViaThinkSoft\OIDplus\OIDplusPagePublicResources->gui()
#2 .../index.php(62): ViaThinkSoft\OIDplus\OIDplusGui->generateContentPage()
#3 {main}