diff --git a/extras/rhubarb-for-spine/src/main/kotlin/com/rhubarb_lip_sync/rhubarb_for_spine/AnimationFileModel.kt b/extras/rhubarb-for-spine/src/main/kotlin/com/rhubarb_lip_sync/rhubarb_for_spine/AnimationFileModel.kt
index 53f496e..7b2cc63 100644
--- a/extras/rhubarb-for-spine/src/main/kotlin/com/rhubarb_lip_sync/rhubarb_for_spine/AnimationFileModel.kt
+++ b/extras/rhubarb-for-spine/src/main/kotlin/com/rhubarb_lip_sync/rhubarb_for_spine/AnimationFileModel.kt
@@ -27,7 +27,7 @@ class AnimationFileModel(animationFilePath: Path, private val executor: Executor
 		mouthShapes = if (mouthSlot != null) {
 			val mouthNames = spineJson.getSlotAttachmentNames(mouthSlot)
 			MouthShape.values().filter { mouthNames.contains(mouthNaming.getName(it)) }
-		} else null
+		} else listOf()
 
 		mouthSlotError = if (mouthSlot != null) null
 		else "No slot with mouth drawings specified."
@@ -75,6 +75,19 @@ class AnimationFileModel(animationFilePath: Path, private val executor: Executor
 	}
 	val busy by busyProperty
 
+	val validProperty = SimpleBooleanProperty().apply {
+		val errorProperties = arrayOf(mouthSlotErrorProperty, mouthShapesErrorProperty)
+		bind(object : BooleanBinding() {
+			init {
+				super.bind(*errorProperties)
+			}
+			override fun computeValue(): Boolean {
+				return errorProperties.all { it.value == null }
+			}
+		})
+	}
+	val valid by validProperty
+
 	private fun saveAnimation(mouthCues: List<MouthCue>, audioEventName: String) {
 		val animationName = getAnimationName(audioEventName)
 		spineJson.createOrUpdateAnimation(mouthCues, audioEventName, animationName, mouthSlot, mouthNaming)
@@ -94,8 +107,13 @@ class AnimationFileModel(animationFilePath: Path, private val executor: Executor
 		if (missingBasicShapes.isEmpty()) return null
 
 		val result = StringBuilder()
-		result.append("Mouth shapes ${missingBasicShapes.joinToString()}")
-		result.appendln(if (missingBasicShapes.count() > 1) " are missing." else " is missing.")
+		val missingShapesString = missingBasicShapes.joinToString()
+		result.appendln(
+			if (missingBasicShapes.count() > 1)
+				"Mouth shapes $missingShapesString are missing."
+			else
+				"Mouth shape $missingShapesString is missing."
+		)
 
 		val first = MouthShape.basicShapes.first()
 		val last = MouthShape.basicShapes.last()
diff --git a/extras/rhubarb-for-spine/src/main/kotlin/com/rhubarb_lip_sync/rhubarb_for_spine/MainView.kt b/extras/rhubarb-for-spine/src/main/kotlin/com/rhubarb_lip_sync/rhubarb_for_spine/MainView.kt
index 76a0823..b797d13 100644
--- a/extras/rhubarb-for-spine/src/main/kotlin/com/rhubarb_lip_sync/rhubarb_for_spine/MainView.kt
+++ b/extras/rhubarb-for-spine/src/main/kotlin/com/rhubarb_lip_sync/rhubarb_for_spine/MainView.kt
@@ -1,5 +1,8 @@
 package com.rhubarb_lip_sync.rhubarb_for_spine
 
+import javafx.beans.binding.Bindings
+import javafx.beans.property.Property
+import javafx.beans.property.SimpleBooleanProperty
 import javafx.beans.property.SimpleStringProperty
 import javafx.event.ActionEvent
 import javafx.event.EventHandler
@@ -77,6 +80,7 @@ class MainView : View() {
 		}
 		fieldset("Audio events") {
 			tableview<AudioFileModel> {
+				placeholder = Label("There are no events with associated audio files.")
 				columnResizePolicy = SmartResize.POLICY
 				column("Event", AudioFileModel::eventNameProperty)
 					.weigthedWidth(1.0)
@@ -112,6 +116,10 @@ class MainView : View() {
 											val audioFileModel = this@tableview.items[index]
 											audioFileModel.performAction()
 										}
+										val invalidProperty: Property<Boolean> = fileModelProperty
+											.select { it!!.validProperty }
+											.select { SimpleBooleanProperty(!it) }
+										disableProperty().bind(invalidProperty)
 									}
 								else
 									null