this happened to me aswell and it was dued to images which where 0 bytes at the end of the file or in the middle.. any way.. do to it simply open the hh8 program, dont move down with the images but simply hit the Export All button.. then press the ... button to choose a destination folder.. and press Export..
when the export has ended close hh8 and open the folder.. your pc might slow down a bit since you are saying there are a lot of images into that wil so be patient... now order the files doing right mouse click -> arrange icon by -> dimension.. now files should be ordered with the lowest first and the biggest last..
press the first file and check that it is 1,05kb and that it is a 4x1 image made of a black small line.. just like this file i attached..
if it is not.. and if the file you are looking at is totally empty and is a 0kb file then keep doing on until you find a file as i said.. when u find it you will have to delete all the files which where 0kb before it and copy it renaming them the same way..
then open hh8 and rebuild it using the create new button, to activate it you must have the same wil have you have exported open, press the create button and choose the folder where u have all the images and choose a file name different from the original, leave placement from file and images system. after u have created the file try opening it to see if the problem persists.. if it does zip the wil and send it to me.. i will give you my email in private