This most likely indicates a problem with the Meter Aiming settings of the calculation grid in question.  Typically for Unified Glare Rating (UGR), you want to choose one of the Vertical options shown below (the same direction an observer would be looking).  

If you leave the meter aiming at the default of "Normal", UGR calculations are invalid for a horizontal grid and ElumTools will report them as 10 (for historical compatibility with AGi32). 

It may also be helpful to peruse the AGi32 help on UGR which gives a good overview of the technical background behind UGR.