The jdk directory should point to the directory itself. I myself am running vista and my path looks like this: C:\Program Files (x86)\Java\jdk1.6.0_19
I am not sure why java would do such a thing, maby to poll for updates? But you might want to look further for that.
A logging message reports there is some time limit on this version of Mendix. What is the limit and what happens when it expires?
This sounds like you have the community version of Mendix. This version has a maximum time limit for the uptime of the xas. I believe the current time limit is 2 hours. But once again i am not totally sure.
Good news - downloading the SDK again has fixed the problem!
Couple of points:
1) My firewall reports "Java Platform SE binary is trying to act as a server and accept incoming connections" Should I allow it to do this?
2) A logging message reports there is some time limit on this version of Mendix. What is the limit and what happens when it expires?
1) My firewall reports "Java Platform SE binary is trying to act as a server and accept incoming connections" Should I allow it to do this?
Yes, otherwise your browser would not be able to connect to the Mendix server. The Java Platform SE binary in fact represents every java process, as far as Windows knows, since Java is actual a kind of virtual machine, and each java application runs inside this 'Java Platform'. Note that therefore the firewall settings apply for every Java process you are running. (Java has its own security manager in which you can restrict the permissions of individual Java processes).