Hi there hiroyuki718,,,,,
The question I would like to ask is :
Q1. Why are you still using this old version ????
Q2- Why dont you upgrade the client to version 7??
Any why if you ever plan to go for it just do the following :
On the Lotus Notes domino server console run the following command
Load convert -d -u mail\(put here the file name of the 5.01 client) * mail7.ntf
This command is for upgrading the template and you can just uninstall client 5.0.1 and reinstall client 7 then check .
You know that last Dec IBM issued version 8.5 .
Good Luck