Major problems images into Word

Hi all,

At the moment I am having major issues with inserted images into word. Background: it concerns my PhD thesis of about 140 pages. In this document I have inserted about 10-15 TIFF images. I had some resolution problems with the printout of my first draft, which made me decide to increase the resolution of my images and re-insert them into word. The images were made in Illustrator and then exported as TIFF images. Result: a word document that is very large (46 MB at the moment).

The type of issue is different every moment, but here are some of the issues I have experienced:
- instead of the image a white box with a small red cross inside and the message "This image cannot currently be displayed." However, when I close the document and re-open it, the image sometimes re-appears. But then, often a different image would have disappeared instead. So at any moment, there always are some pictures missing, whereas others are gone.
- when inserting an image, it is downscaled (so not its real size).
- when trying to re-insert the picture, just a white box is inserted without any message.

Could anybody help me out, I am really freaking out :S