Index: lams_central/web/includes/javascript/authoring/authoringGeneral.js
===================================================================
diff -u -rc8630f4a8f378012fc675f9c20aa0426910df206 -r178f91f787e871aec26f8136c47f4def7ba942c2
--- lams_central/web/includes/javascript/authoring/authoringGeneral.js	(.../authoringGeneral.js)	(revision c8630f4a8f378012fc675f9c20aa0426910df206)
+++ lams_central/web/includes/javascript/authoring/authoringGeneral.js	(.../authoringGeneral.js)	(revision 178f91f787e871aec26f8136c47f4def7ba942c2)
@@ -2574,7 +2574,7 @@
 		}
 		layout.modified = modified;
 		if (!modified && layout.activities.length > 0) {
-			$('#previewButton').prop('disabled', layout.ld.invalid);
+			$('#previewButton').prop('disabled', layout.ld.invalid === true);
 			$('#exportLamsButton').removeClass('disabled');
 			$('#ldDescriptionFieldModified').text('');
 		} else {