Two quotes from LSL Wiki :
"It seems like the camera does not always release properly when unsitting an avatar (I would add: Or detaching a HUD, Ataro A.) even though permissions are lost."
"The camera can often not behave as one would desire."
( http://lslwiki.net/lslwiki/wakka.php?wakka=camera )
"Camera not released properly" means: You are stuck in a camera view and you can't get rid of it. Due to lag or whatever, this happens sometimes, but not very often.
What can you do then?
Maybe you left without clicking >> EXIT << ?
Wait until you can click the HUD again and leave with >>EXIT<<.
If not, camera emergency shortcuts may help:
SHIFT-ESC, maybe twice - and/or CTRL-9
Or: Move your avatar some steps forward
or Teleport to another sim (and come back) (works most of the time)
NEW: I found out: If you want to stop the script, rightclick the HUD or prim, choose EDIT -> CONTENT and look for a button named "Reset Scripts". Click it. All should be ok then.