unreliable result from Coloposcopy

Hiya
I had a follow up colposcopy last month after they found CIN 1 and CIN 2 in June. Just got the letter from the hospital today which says “Unfortunately, for technical reasons, it was not possible to get a totally reliable result”
I now have to go back through that painful and uncomfortable biopsy ordeal again. Is this common or am I just very unlucky?