A user on the forums on TheDigitalLifestyle.com reported a problem with a brand new HP Pavilion M7775 running Windows Vista Home Premium and Media Center Extender sessions crashing. The user did all the usual stuff, checked network connections, firewall and AV software but it still kept crashing.
It turns out that the problem could be caused by some pre-installed software. The Picasso add-in steals the focus from Media Center when the Extender session is launched and so instead of the remote controlling Media Center it tries to control Picasso (which is not visible). So pressing the green button should bring Media Center back to the foreground and get round the problem.
A more permanent solution is to remove Picasso ->General->Program Library Options->Edit Program Library and uncheck Picasso and the Front Panel add-in. Then restart the extender session. I haven’t verified this myself but I am told it does fix the problem.
This raises two issues. What is the quality control like a HP and how much "crapware" gets pre-installed on new machines. So my advice is when you get a new machine remove crapware before you start using it!