I realize that this is over 5 years late, but if you deal with 17025 PT issues, this becomes important, and it's never the wrong time to bone up on 17025 issues!
Buckle up, folks!
The En number is merely a percentage of your measured value to the reference value, corrected with the square root of the sum of the squares of your uncertainty and the uncertainty of the reference value.
If your absolute En number is over 1, then your corrected measurement is GREATER than your uncertainty. That would indicate 1 or a combination of four causes, assuming your reference value and reference uncertainty are valid:
1) Your uncertainty is incorrect
2) Your measurement is incorrect
3) Your measurement equipment is faulty
4) Your measurement procedure is faulty
1 and 2 are most often typos on your part, and are easily corrected. 3 and 4 are system issues that MUST be addressed in some way prior to your next 17025 audit, and would ultimately require a corrective action.
Also, the .pdf posted above is a good calculation reference. I recommend saving it for your convenience.
I hope this helps someone save some time and heartache!