Can't drag a bezigon close to the edge of the drawing, or the computer beeps attempting to smooth a bezigon or polygon which is close to the edge of the drawing.
Drag the polygon/bezigon away from the edge of the drawing.
The bounding box of a bezigon or smoothed polygon is larger than a regular polygon. (The bounding box is an invisible rectangle that defines the outer boundaries of all objects. When you select an object, the four resize handles that appear are at the corners of the bounding box.)
Draw a polygon, and notice that the four resize handles are very close to the visible boundary of the polygon. Draw a bezigon with control handles that extend away from the bezigon and notice that the four resize handles are much farther away from the visible boundary of the bezigon. This is because the bounding box that defines the bezigon includes the positions of the control handles. (Select the bezigon, then choose Reshape, then choose Select All to see all the control handles of the bezigon. Notice that the reshape handles just enclose the entire bezigon and the control handles.)
This means that a bezigon might not be able to be placed close to the edge of the drawing, as this would cause the control handles at the corners of the bounding box to be off the drawing. Also, if a polygon or bezigon is placed as close as possible to the drawing edge, you may not be able to smooth the polygon/bezigon. Smoothing causes the bounding box to increase.
{See the graphic for an example. Note, this graphic has been 'faked' to show simultaneously the control handles and the resize handles of the bezigon}