diff --git a/frappy/modules.py b/frappy/modules.py
index 802e2d1..241a9bc 100644
--- a/frappy/modules.py
+++ b/frappy/modules.py
@@ -68,8 +68,8 @@ class Writable(Readable):
             target_dt.compatible(value_dt)
         except Exception:
             if type(value_dt) == type(target_dt):
-                raise ConfigError('the target range extends beyond the value range') from None
-            raise ProgrammingError('the datatypes of target and value are not compatible') from None
+                raise ConfigError(f'{name}: the target range extends beyond the value range') from None
+            raise ProgrammingError(f'{name}: the datatypes of target and value are not compatible') from None
 
 
 class Drivable(Writable):
diff --git a/frappy/secnode.py b/frappy/secnode.py
index 65dc633..73cb56b 100644
--- a/frappy/secnode.py
+++ b/frappy/secnode.py
@@ -27,6 +27,7 @@ from frappy.dynamic import Pinata
 from frappy.errors import ConfigError, NoSuchModuleError, NoSuchParameterError
 from frappy.lib import get_class
 from frappy.version import get_version
+from frappy.modules import Module
 
 
 class SecNode:
@@ -131,6 +132,9 @@ class SecNode:
                     # creation has failed already once, do not try again
                     return None
                 cls = classname
+            if not issubclass(cls, Module):
+                self.errors.append(f'{cls.__name__} is not a Module')
+                return None
         except Exception as e:
             if str(e) == 'no such class':
                 self.errors.append(f'{classname} not found')