Image upload problem on IIS

Hi, I have problem uploading images to the blog hosted on IIS server. At first, there’s some database problem. when i check the upload folder, i see the uploaded image and its associated thumbnail. but there was error writing to database. I search the forum and found the solution at http://wordpress.org/support/topic/78384 basically it tell us to do the following:

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You have to set the value of 3 Columns from “NOT NULL” to “NULL”..
the columns are located in the table “wp_posts” and are named as follows:
“to_ping”
“pinged”
“post_content_filtered”
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after i set the columns to NULL, the upload worked and the images are showing after i upload them. however, another problem surfaced. thumbnails are not generated. i check the upload folder, there is the uploaded image, but not the thumbnail.

i found a post that says increasing the memory in php.ini would help. so i did that but the thumbnail generation still didnt happen. i am just wondering why after i set the NULL to those columns then thumbnail generation just stopped. any suggestions/advices?

thanks in advance for any help =)
j