normally.....
Windows Vista: Put the two files (Layer Mask.atn, Layer Mask.png) in the folder:
C:\ProgramData\Adobe\Photoshop Elements\6.0\Photo Creations\photo effects
Then, delete the following file:
C:\ProgramData\Adobe\Photoshop Elements\6.0\Locale\en_US\MediaDatabase.db3
Windows XP: Put the two files (Layer Mask.atn, Layer Mask.png) in the folder:
C:\Documents and Settings\All Users\Application Data\Adobe\Photoshop Elements\6.0\Photo Creations\photo effects
Then, delete the following file:
C:\Documents and Settings\All Users\Application Data\Adobe\Photoshop Elements\6.0\Locale\en_US\MediaDatabase.db3
Alternatively contact support