I had this same problwm, worked out I must have cloned the line as an instance instead of a copy. I had to click the make unique button (under the modifier stack list area). Then adding the edit poly modifier worked as expected. Hope it helps 🙂
I've had this exact same problem and have solved it by NOT creating the spline in a Perspective view.
If I create the spline, for example, in a Front viewport, there is no problem and the Spline converts to a Editable Poly 🙂
Hope that helps 🙂
your spline should be closed, check for overlapping vertices, once your spline is closed, you can throw an Edit Ploy modifier an you will hava a plane
I figured this out ... because i had same problem .. i was making a baroque ornament and no matter what i tried it ether dissapired or turned in to a hollow shape . BUT the solution here is that when you have more complex shapes the verts might over lap somwehere. so edit the line dots and make sure no lines cross and it makes clean shape specially those sneaky little corners . once you have done that applying edit poly works like a charm and it turns in to a solid peace . 🙂
thanks
whats is the differance between convert to edit poly or add modifier for performace ?
I have had similar problems quite a number of times and although trying to use the extrude modifier or the enabling in viewport doesn't give me quite the results I wanted. I found out that the problem was that the spline was not a complete closed spline. The solution, I went to each independent vertice to confirm whether it is welded to the spline vertices and it has worked