moving a custom stamp to different location on page after placement

I am using acrobat 8.1 pro to review architectural drawings. I created a custom stamp of a mechanical plans so that I could overlay it on the floor plan. I thought it was working fine as i was able to place a stamp on a drawing, however when the plans did not line up, I had trouble moving it once it was placed. I have tried using both the select and the hand tool. Once selected, it is highlighted and when the cursor is over a line it changes to the 4way arrow cursor, but as I hold down the left mouse button to drag it, it changes to a crossed out circle cursor and will not move. It it because my stamp is as large as the page that I am stamping? How can i move the stamp after placing it?