[budney]

Sounds like you are using the CHT lockscreen? If so read this:

About the CHT lockscreen:
Currently, the CHT lock screen does not support any PIN code or password protected unlocking.
Remove any unlock codes before turning on the CHT lockscreen or you will be permanently locked out of your device and you'll have to do a hard reset.
If you are using a gsensor app to automatically rotate the screen and you have it to always rotate, you should add the class "CHTLockscreen" to the exception list.
If you don't have the rotation app set rotate everything, but only a list of desired programs, then you don't have anything to worry about.
If you need to lock the CHT lockscreen externally, you can do it with this: "\Windows\CHT_Helper.exe -lock"

CHT lockscreen for WM6.1:
I've prepated an addon cab with an alternative CHT lockscreen for WM6.1 users.
Installing the addon cab will revert the CHT lockscreen to the older lock system used in v1.7.x. The downside of this is that the old lock system carries with it some flaws:
on some devices it might not lock all hardware keys, has a slower lock response on wakeup, on longer calls it might relock before the call is over, gsensor apps that rotate manila will also rotate it, doesn't integrate with the WM6.5 lock system (softkey in start menu, button assigned lock).
Of course, for those who really want to use the CHT lockscreen and don't mind those shortcomings, the ultimate upside is that is does work on WM6.1.
Thanks to Kenia1234 for testing the WM6.1 lockscreen.
Download it here. - Do NOT install this on WM6.5. This is only for WM6.1.

http://forum.xda-developers.com/showthread.php?t=625483