I am having trouble cutting black Stahls Econoprint with my GCC Puma III. The sizing media does not seem to be able to identify the vinyl. It tries, but then stops and does not correctly read. When I did get it to size the media, the cuts typically stop partially through. Is there something reflective in the black backing that confuses the reader? I do not have this problem with siser easyweed nor eco film from imprintables. I also had no problems cutting Red Econoprint. I have actually tried moving my light source around thinking it may be fooling the sensor. No luck...