I don't know why iTunes would suddenly stop letting you drag & drop! Try adding files this way instead:

Within LW tools > options > saving. Within the text field is the location of your saved folder (by default C:\Documents and Settings\your name\Shared).

Now within iTunes, file > add file to library. You'll see 'look in', go through & find your saved folder. When your songs appear, click on a song > open. That song will be transferred to your iTunes library! To move a block of files, click on the first file, hold down the shift key & click on the last file. Now click open & the block will be transferred to iTunes