SMP only single player works fine.
Within a minute of the lumberjack becoming active the server reboots.
No log reported for the error
As soon as you try and log back into the server it will reboot again.
Only way to get out of the loop is to load a backup world.

@Korizan - are you using MCPC+/Cauldron?

A straight forge install. I went ahead and put the server directly on my own machine with a new world and got the same result. Tryed it again with debug on but then it just ground everything down but it didn't freeze and restart. Any ideas on what to try now ? Is it the forge version (1207) ?

Tryed Forge 1230 same result. Starting to wonder if it is Railcraft that already eats resources, and when you combine that with a robot AI the server chokes and resets (complete guess, will test some more later on unless someone else comes up with something else to try)

I guess I re reported this issue but ya this is happening with cauldron also and no there is no report at all

There should be some kind of report. Try /with/ Cauldron, as it tends to be better at catching deadlocks.

Okay buildcraft ONLY no other mods installed same result. brand new world.
No mod conflict. Replicated about 7 times.
It appears to be an issue when it first leaves the docking station to decide its first target but most of the time is when it finishes the first tree and starts trying to figure out where to go next and that is where the lockup occurs. Sorry that is the best I can do, hope it helps.

In my case is was with a delivery robot and yes it happens when the robot seem to have found a valid task