Different users have reported different success with various measures over this issue. Try these out:
Install the patch
Install HoW (patch included)
Empty the cache folders in the IWD directory
Increase the cache size in the IWD setup
Create a new folder in your IWD directory and call it something like Override2. Copy all of the files from the original Override folder into Override2. Delete all the files in your original Override folder. On arrival at Easthaven, save and exit the game. Copy all the files from Override2 back into your original Override folder and delete Override2. (last resort - special thanks to Yshania ).
Thanks to Gruntboy for this!