Recurring error: “Not enough landmarks selected to find a transformation model”.

[rmd13]

I am using Fiji to do landmark correspondence registration, most of the time it is ok, however, sometimes it frequently shows error nomatter how many time I tried:
“Not enough landmarks selected to find a transformation model”. even if I am pointing the same number of points in the same position on the same images.
I have to restart Fiji. Is there a cause for this problem?