The "Please enter an integer between 2 and 256" message typically appears when the Fractions - Denominator value in the is set to a value of 1. It is possible to continue measuring by enabling fractions and changing this integer value to any value above 1, as the message implies.
The value of 1 populated in the fractions field may be saved in one's template. If so, modify the template to remove this value. Please see the attached image.
Thank you, it appears to have fixed the issue.
How it came about however is still a complete mystery. To gain access to the fractions dialogue I had to set the units to inches (in all metric units it remained greyed out). I have never intentionally used inches in the measure command, maybe a stray mouse click and scroll got it.