Before you will you this theme go to "var/mobile/Library/Caches/"  :

For 4.1 users :
- Delete "com.apple.Springboard.folderSwitcherLinen" file. 

For 4.2.1 users :
- Delete > 

com.apple.SpringBoard.folderSwitcherLinen.0
com.apple.SpringBoard.folderSwitcherLinen.1
com.apple.SpringBoard.folderSwitcherLinen.2
com.apple.SpringBoard.folderSwitcherLinen.3
