In SharePoint, sometimes generates an error when you try to edit in datasheet view some list. Your browser freezes and you have to close it and re-open the site. If this situation happens you can try to solve this applying this solutions:
In my case, these solutions not solved my problem. If you create your own master page it's probably you've created a foot page. This is a common situation but if put an image bigger than 19px of height you couldn't edit your lists in datasheet view in IE6. Try putting an 19px-of-height image in your master page and the problem will solve.