diff --git a/src/com/bytezone/diskbrowser/applefile/DoubleHiResImage.java b/src/com/bytezone/diskbrowser/applefile/DoubleHiResImage.java
index 0fcd92f..e7de067 100644
--- a/src/com/bytezone/diskbrowser/applefile/DoubleHiResImage.java
+++ b/src/com/bytezone/diskbrowser/applefile/DoubleHiResImage.java
@@ -25,7 +25,7 @@ public class DoubleHiResImage extends HiResImage
   {
     super (name, buffer);
 
-    assert name.endsWith (".PAC") || name.endsWith ("A2FC");
+    //    assert name.endsWith (".PAC") || name.endsWith ("A2FC");
 
     if (name.endsWith (".PAC"))
     {
@@ -35,17 +35,17 @@ public class DoubleHiResImage extends HiResImage
       auxBuffer = doubleScrunch.memory[0];
       this.buffer = doubleScrunch.memory[1];
     }
-    else if (name.endsWith (".A2FC"))
+    else          //if (name.endsWith (".A2FC") || auxType == 0x2000)
     {
       auxBuffer = new byte[0x2000];
       this.buffer = new byte[0x2000];
       System.arraycopy (buffer, 0, auxBuffer, 0, 0x2000);
       System.arraycopy (buffer, 0x2000, this.buffer, 0, 0x2000);
     }
-    else
-    {
-      auxBuffer = null;
-    }
+    //    else
+    //    {
+    //      auxBuffer = null;
+    //    }
 
     createImage ();
   }
diff --git a/src/com/bytezone/diskbrowser/applefile/OriginalHiResImage.java b/src/com/bytezone/diskbrowser/applefile/OriginalHiResImage.java
index 6398581..b6b7850 100755
--- a/src/com/bytezone/diskbrowser/applefile/OriginalHiResImage.java
+++ b/src/com/bytezone/diskbrowser/applefile/OriginalHiResImage.java
@@ -107,7 +107,6 @@ public class OriginalHiResImage extends HiResImage
         int val = (value >> px) & 0x01;         // get the next pixel to draw
         int column = (ptr + px) % 2;            // is it in an odd or even column?
         line[linePtr++] = val == 0 ? 0 :        // black pixel
-        //  palette[colourBit][column];         // coloured pixel - use lookup table
             colours[paletteTable[colourBit][column]]; // coloured pixel - use lookup table
       }
     }
diff --git a/src/com/bytezone/diskbrowser/disk/AppleDisk.java b/src/com/bytezone/diskbrowser/disk/AppleDisk.java
index ec258b4..87923e9 100755
--- a/src/com/bytezone/diskbrowser/disk/AppleDisk.java
+++ b/src/com/bytezone/diskbrowser/disk/AppleDisk.java
@@ -503,7 +503,7 @@ public class AppleDisk implements Disk
   @Override
   public boolean isValidAddress (DiskAddress da)
   {
-    return isValidAddress (da.getTrack (), da.getSector ());
+    return da != null && isValidAddress (da.getTrack (), da.getSector ());
   }
 
   /*
diff --git a/src/com/bytezone/diskbrowser/disk/DiskFactory.java b/src/com/bytezone/diskbrowser/disk/DiskFactory.java
index e35ba2f..bdcf2d9 100755
--- a/src/com/bytezone/diskbrowser/disk/DiskFactory.java
+++ b/src/com/bytezone/diskbrowser/disk/DiskFactory.java
@@ -229,14 +229,22 @@ public class DiskFactory
 
     if (suffix.equals ("woz"))
     {
-      WozDisk wozDisk = new WozDisk (file);
-      AppleDisk appleDisk256 = new AppleDisk (wozDisk, 35, 16);
-      disk = checkDos (appleDisk256);
-      if (disk == null)
-        disk = checkProdos (new AppleDisk (wozDisk, 35, 8));
-      if (disk == null)
-        disk = new DataDisk (appleDisk256);
-      return disk;
+      try
+      {
+        WozDisk wozDisk = new WozDisk (file);
+        AppleDisk appleDisk256 = new AppleDisk (wozDisk, 35, 16);
+        disk = checkDos (appleDisk256);
+        if (disk == null)
+          disk = checkProdos (new AppleDisk (wozDisk, 35, 8));
+        if (disk == null)
+          disk = new DataDisk (appleDisk256);
+        return disk;
+      }
+      catch (Exception e)
+      {
+        System.out.println (e);
+        return null;
+      }
     }
 
     if (suffix.equals ("v2d"))
diff --git a/src/com/bytezone/diskbrowser/disk/SectorList.java b/src/com/bytezone/diskbrowser/disk/SectorList.java
index 93f9dc2..7b104f5 100755
--- a/src/com/bytezone/diskbrowser/disk/SectorList.java
+++ b/src/com/bytezone/diskbrowser/disk/SectorList.java
@@ -22,6 +22,8 @@ public class SectorList extends AbstractFile
 
     for (DiskAddress da : sectors)
     {
+      if (!disk.isValidAddress (da))
+        break;
       byte[] tempBuffer = disk.readSector (da);
       System.arraycopy (tempBuffer, 0, buffer, ptr, disk.getBlockSize ());
       ptr += disk.getBlockSize ();
diff --git a/src/com/bytezone/diskbrowser/disk/WozDisk.java b/src/com/bytezone/diskbrowser/disk/WozDisk.java
index a0c8cf9..c6c3040 100644
--- a/src/com/bytezone/diskbrowser/disk/WozDisk.java
+++ b/src/com/bytezone/diskbrowser/disk/WozDisk.java
@@ -24,20 +24,22 @@ class WozDisk
   // constructor
   // ---------------------------------------------------------------------------------//
 
-  public WozDisk (File file)
+  public WozDisk (File file) throws Exception
   {
     this.file = file;
     Nibblizer nibbler = new Nibblizer ();
     byte[] buffer = readFile ();
 
-    assert matches (header, buffer);
+    if (!matches (header, buffer))
+      throw new Exception ("Header error");
 
     int cs1 = readInt (buffer, 8, 4);
     int cs2 = Utility.crc32 (buffer, 12, 256 - 12 + 35 * TRK_SIZE);
     if (cs1 != cs2)
     {
-      System.out.printf ("Checksum: %08X%n", cs1);
-      System.out.printf ("Calculat: %08X%n", cs2);
+      System.out.printf ("Checksum  : %08X%n", cs1);
+      System.out.printf ("Calculated: %08X%n", cs2);
+      throw new Exception ("Checksum error");
     }
 
     int ptr = 12;
diff --git a/src/com/bytezone/diskbrowser/prodos/FileEntry.java b/src/com/bytezone/diskbrowser/prodos/FileEntry.java
index 10ccb7b..d121cec 100755
--- a/src/com/bytezone/diskbrowser/prodos/FileEntry.java
+++ b/src/com/bytezone/diskbrowser/prodos/FileEntry.java
@@ -293,7 +293,8 @@ class FileEntry extends CatalogEntry implements ProdosConstants
             else
               file = new DoubleHiResImage (name, exactBuffer, link.getBuffer ());
           }
-          else if (name.endsWith (".PAC") || name.endsWith (".A2FC"))
+          else if (name.endsWith (".PAC") || name.endsWith (".A2FC")
+              || (endOfFile == 0x4000 && auxType == 0x2000))
             file = new DoubleHiResImage (name, exactBuffer);
           else if ((endOfFile == 0x1FF8 || endOfFile == 0x1FFF || endOfFile == 0x2000
               || endOfFile == 0x4000)