I've been building my module.. few areas done and as I was testing it a skeleton warrior suddenly teleported out of nowhere.. I have not done any hostile creatures yet so I was bit suprised. As I ran like hell (my test character level 1) I luckily came up to some town folks who I HAD created there. Well they started fighting.. town people vs the skeleton warrior, but got beaten pretty easily.
Now back to the actual issue.. where the %&#! did that skeleton warrior come? :o Like I said I've only done terrain and objects no other creatures than small band of those town people. It's raining and some storm in the town, but that shouldn't trigger any such events, right?
I havent tried again does the skeleton always teleport out of nowhere, but damn I was suprised. :)

Check to make sure that there isn't set up as a random encounter that skeleton. Should be under the tools button.

Some of the placeables like zombie corpses, skeleton bones and gargolyes come in two modes. One triggers whenever a PC comes near and the other stays as what you placed. It sounds like you placed skeleton bones (reanimate) down. So be sure to check the properties on items when you place them.

Yeah, one guy simulated an old battlefield by placing 50 or so skel bones down. When he tested by walking through they ALL animated - instant minefield LOL! :D

Yup that was the thing.. noticed it last night. I had a pile of bones lying around in there. :)
Damn for a second I thought my module started to live on it's own.. skeleton appearing out of nowhere into middle of band of slavers and they started fighting. :)