We use TightVNC for connecting into home workers machines when troubleshooting and came across a problem with one particular user – occasionally we could not connect.
We discovered that their machine was using Fast User Switching – husband and wife who had separate accounts.
When both are logged on e.g. the wife logged on early morning and then our worker logged on later in the day TightVNC was not connecting but when only one of them was logged on it did connect.
What is happening is that the user you’re logging on as is getting assigned a “session” other than session zero, and the TightVNC server is then restoring session zero to the console because that’s the session it’s capable of remoting.
You should be able to fix things by logging off all of the users from the XP system and then re-connecting via TightVNC. We came across no other way around this problem.