--- tw_import/tw_import_delimited_orig.module	2010-05-17 13:09:02.000000000 -0400
+++ tw_import/tw_import_delimited.module	2010-05-20 00:37:23.000000000 -0400
@@ -122,9 +122,19 @@ function tw_import_delimited_tw_form_sub
       $columns[] = tw_quote_identifier($colname);
     }
     // TODO: Option to append instead of replace (i.e., skip the TRUNCATE)
+  //only truncate this table if it exists and is already managed by {tw_tables}
     if (db_table_exists($tablename)) {
-      db_query('TRUNCATE TABLE {' . $tablename . '}');
-      $prevexists = TRUE;
+      $sql = "SELECT twtid FROM {tw_tables}
+              WHERE dbconnection='%s' AND tablename='%s'";
+      $twtid = db_result(db_query($sql, $dbconnection, $tablename));
+      if ($twtid) {
+        db_query('TRUNCATE TABLE {' . $tablename . '}');
+        $prevexists = TRUE;
+      }
+      else {
+        drupal_set_message(t('"!tablename" is not a table managed by Table Wizard.  For initial import, please choose a table name that is not in use', array('!tablename' => $tablename)));
+        return NULL;
+      }
     }
     else {
       // Note that when using table prefixes, a prefix is prepended to the table name