I have never come across this so these are suggestions only.
Is it the same if you use a different computer? Have you stopped and restarted the application servers (all of them) Have you cleared the client cache Have you cleared the server cache (rename the server cache folder) If you give admin rights to another user account and log on with that do you get the same problem Have you changed anything on the server recently e.g. updated java etc.
Funny as it sounds Mark Shanker I had the exact same problem as Shanker yesterday, you need close SD client and clear the cache, reopen the client and you should have the fields visible to be able to drop them onto the form you want.