Body field is required error when creating a new node

When I create a new node, I cannot upload images to imagefield via FUpload. Steps to create:
1) Click on create a new contemt to create a story
2) Fill in the title and body fields
3) Click on Fupload button and select a single picture. "Image queued." message appears.
4) Click on Save button

Result:
Files get uploaded and on the same form this error message appears:

Body field is required.
All queued images were deleted.

I also tried with imagefield widget (replaced with fupload widget) and uploaded the same picture and wrote the same title and body. I could create the node without any problems with imagefield widget, so there should be a problem with fupload.