I found the following thread in the Lenovo forums, that sounds like the same problem, and indicates you need to turn the num lock off. See
here.and
here.
If that doesn't do it,
here's the keyboard troubleshooter for your Thinkpad. It's possible a bios update could be in order. It's also possible you need to check the internal connection. If you decide to do so,
here's a link to the service manual for that model.
I hope this information allows you to resolve this issue. If you need further assistance, please post back with a comment to this thread.
If I've managed to answer your question or solve a problem, please take just a moment to rate this post....thanks!