Look in the file for entries similar to:
Code:
<Window Name="RewardPack_clone_0" alignment="1" alignment_offset="9,187" size="334,313">
<Properties clone_version="4" />
</Window>
You might have several of them. Backup your UI settings file and then just delete all these
RewardPack_clone_# entries. In this case I would delete all three lines.
When you start the game, the Quest window will appear in its default location near the top-left edge of the screen (does for me) and then move it where you want it. Sometimes the game gets confused if there are too many entries.
Hope that helps