Hello everyone
I had sometimes the same problem in sharp-bending splines.
After checking everything, I found out that the problem :
Original Program :
(setq pt (vlax-curve-getclosestpointto s po nil))
(setq di (vlax-curve-getdistatpoint obj pt))
Modified Program :
(setq pt (vlax-curve-getclosestpointto s po nil))
(setq pt (vlax-curve-getclosestpointto s pt nil))
(setq di (vlax-curve-getdistatpoint obj pt))
The middle line doesn't seem to be necessary, BUT It's Necessary !!
It is not logical, but it works !!!