sp does not return all fields in Report Data window

Hi,
In the ssrs report, I am using a stored proc sp1.
When I add this to the dataset, automatically, it shows the fields that the sp1 ertrieves.
Now, I have made a slight modification in the sp1 which gives me an extra field as well as all the previous fields.
But now, when I click on ok in the datasets designer for this sp1, I only get one field.
Do you know why I do not see other fields in the sp1?
Note that if I run the sp1 in the query analyser, it retrieves all fields.
Any thoughts please?
Thanks