Index: trunk/src/scriptbuilder/structures/TimeSlice.java
===================================================================
--- trunk/src/scriptbuilder/structures/TimeSlice.java	(revision 48)
+++ trunk/src/scriptbuilder/structures/TimeSlice.java	(revision 57)
@@ -181,17 +181,17 @@
     public int compareTo(Object o)
     {
-        TimeSlice other = (TimeSlice) o;
-        if (this.getTime() < other.getTime())
-        {
-            return -1;
-        }
-        else if (this.getTime() > other.getTime())
-        {
-            return 1;
-        }
-        else
-        {
-            return 0;
-        }
+        if (o instanceof TimeSlice)
+        {
+            TimeSlice other = (TimeSlice) o;
+            if (this.getTime() < other.getTime())
+            {
+                return -1;
+            }
+            else if (this.getTime() > other.getTime())
+            {
+                return 1;
+            }
+        }
+        return 0;
     }