diff --git a/screening/source/java/ch/systemsx/cisd/openbis/dss/etl/Hdf5ThumbnailGenerator.java b/screening/source/java/ch/systemsx/cisd/openbis/dss/etl/Hdf5ThumbnailGenerator.java
index 9b666e2eb49b34f8e91e45ffbe69395c8d44d472..d2701402984cad156206ae84a9c5ab7794eee44e 100644
--- a/screening/source/java/ch/systemsx/cisd/openbis/dss/etl/Hdf5ThumbnailGenerator.java
+++ b/screening/source/java/ch/systemsx/cisd/openbis/dss/etl/Hdf5ThumbnailGenerator.java
@@ -385,8 +385,8 @@ public class Hdf5ThumbnailGenerator implements IHDF5WriterClient
         if (result.isOK() == false)
         {
             throw new IOException(String.format(
-                    "Error calling 'convert' for image '%s'. Exit value: %d, I/O status: %s",
-                    imageFilePath, result.getExitValue(), result.getProcessIOResult().getStatus()));
+                    "Error calling 'convert' with parameters %s for image '%s'. Exit value: %d, I/O status: %s",
+                    params, imageFilePath, result.getExitValue(), result.getProcessIOResult().getStatus()));
         } else
         {
             if ((imageDataSetStructure.getChannelColorComponents() != null && imageDataSetStructure
diff --git a/screening/source/java/ch/systemsx/cisd/openbis/plugin/screening/shared/dto/PlateDimensionParser.java b/screening/source/java/ch/systemsx/cisd/openbis/plugin/screening/shared/dto/PlateDimensionParser.java
index 7ccc8931e9e10e8bfa436ab734ff498bf08714cf..847a1f069de83d4e6d16e0a6fc26e943e9e5191a 100644
--- a/screening/source/java/ch/systemsx/cisd/openbis/plugin/screening/shared/dto/PlateDimensionParser.java
+++ b/screening/source/java/ch/systemsx/cisd/openbis/plugin/screening/shared/dto/PlateDimensionParser.java
@@ -56,7 +56,10 @@ public class PlateDimensionParser
      */
     public static PlateDimension tryToGetPlateDimension(final IEntityProperty[] properties)
     {
-        assert properties != null : "Unspecified properties";
+        if (properties == null)
+        {
+            return null;
+        }
         IEntityProperty plateGeometryProperty =
                 EntityHelper.tryFindProperty(properties, PLATE_GEOMETRY_PROPERTY_NAME);
         if (plateGeometryProperty == null)