Clear IfcStore when you load a new file. See #1222.

src/ifcblenderexport/blenderbim/bim/module/aggregate/ui.py

@@ -1,5 +1,6 @@
 from bpy.types import Panel
 from blenderbim.bim.module.aggregate.data import Data
+from blenderbim.bim.ifc import IfcStore
 
 
 class BIM_PT_aggregate(Panel):
@@ -15,6 +16,8 @@ class BIM_PT_aggregate(Panel):
         props = context.active_object.BIMObjectProperties
         if not props.ifc_definition_id:
             return False
+        if not IfcStore.get_file().by_id(props.ifc_definition_id).is_a("IfcObjectDefinition"):
+            return False
         if props.ifc_definition_id not in Data.products:
             Data.load(props.ifc_definition_id)
         if not Data.products[props.ifc_definition_id]:

src/ifcblenderexport/blenderbim/bim/module/material/ui.py

@@ -27,7 +27,12 @@ class BIM_PT_object_material(Panel):
 
     @classmethod
     def poll(cls, context):
-        return bool(context.active_object.BIMObjectProperties.ifc_definition_id)
+        props = context.active_object.BIMObjectProperties
+        if not props.ifc_definition_id:
+            return False
+        if not hasattr(IfcStore.get_file().by_id(props.ifc_definition_id), "HasAssociations"):
+            return False
+        return True
 
     def draw(self, context):
         self.file = IfcStore.get_file()