QTR-Quadtone RIP

I was making a linearisation today with the following values from a 
51-step and got the above error message and the curve was not created:
0.06
0.08
0.1
0.12
0.15
0.17
0.2
0.23
0.26
0.29
0.33
0.36
0.41
0.45
0.48
0.53
0.57
0.61
0.65
0.69
0.72
0.75
0.79
0.83
0.87
0.91
0.95
0.98
1.01
1.04
1.09
1.12
1.14
1.18
1.19
1.22
1.24
1.28
1.31
1.34
1.37
1.4
1.42
1.46
1.49
1.52
1.55
1.57
1.6
1.62
1.69

All the values are increasing albeit not "constantly". If I change the 
penultimate value from 1.62 to 1.63 the curve creation works. Any reason 
this should be so?

Howard