diff --git a/app/controllers/ImportController.asp b/app/controllers/ImportController.asp
index e131ef0..5fde2b1 100644
--- a/app/controllers/ImportController.asp
+++ b/app/controllers/ImportController.asp
@@ -47,7 +47,13 @@ Class ImportController_Class
         up.Upload
 
         If Not Csrf_Valid("import", up.Form("csrf")) Then
-            Flash().AddError "Invalid form state. Please try again."
+            If up.FormElements.Count = 0 Then
+                Flash().AddError "Invalid form state: the upload was not received (" & Request.TotalBytes & " bytes). Please try again."
+            ElseIf Len(up.Form("csrf")) = 0 Then
+                Flash().AddError "Invalid form state: the form token was missing from the upload. Please try again."
+            Else
+                Flash().AddError "Invalid form state: your session expired or changed. Reload this page and try again."
+            End If
             Response.Redirect "/import"
         End If