Hi mybasesp,
To unblock
tbot you've previously blocked, right-click
the tbot account you see on Windows Live Messenger---(you should still be able to see the tbot account with a red slash).
Messenger dialogue box shows up, asking “If unblocked, this contact will be able to have online conversations with you and see your online status”.
Click OK. Then, your tbot should be unblocked.
Let me know if this doesn’t work for you. Thanks. Takako