diff -ur gtg-0.2.4/GTG/taskbrowser/tagtree.py /usr/lib/python2.7/site-packages/GTG/taskbrowser/tagtree.py
--- gtg-0.2.4/GTG/taskbrowser/tagtree.py	2010-04-10 14:38:37.000000000 +0300
+++ /usr/lib/python2.7/site-packages/GTG/taskbrowser/tagtree.py	2010-12-27 18:22:41.457050979 +0200
@@ -356,6 +356,9 @@
         the parent task and the id of the selected task is passed to the
         destination"""
         treeselection = treeview.get_selection()
+        if (treeselection.count_selected_rows() <= 0):
+            return
+
         model, iter = treeselection.get_selected()
         iter_str = model.get_string_from_iter(iter)
         selection.set('gtg/tag-iter-str', 0, iter_str)
diff -ur gtg-0.2.4/GTG/taskbrowser/tasktree.py /usr/lib/python2.7/site-packages/GTG/taskbrowser/tasktree.py
--- gtg-0.2.4/GTG/taskbrowser/tasktree.py	2010-04-10 14:38:37.000000000 +0300
+++ /usr/lib/python2.7/site-packages/GTG/taskbrowser/tasktree.py	2010-12-27 18:23:02.776050978 +0200
@@ -499,6 +499,9 @@
         the parent task and the id of the selected task is passed to the
         destination"""
         treeselection = treeview.get_selection()
+        if (treeselection.count_selected_rows() <= 0):
+            return
+
         model, paths = treeselection.get_selected_rows()
         iters = [model.get_iter(path) for path in paths]
         iter_str = ','.join([model.get_string_from_iter(iter) for iter in iters])