Fire Extinguishers for CO2 - Problems??

I bought a CO2 system including regulator etc from a German Company at the beginning of the year and have been using fire extinguishers for the CO2. I have now had two breakdowns with the regulator, the first time a couple of months ago the German Co sent me a replacement, the second breakdown has happened over the past couple of days. For some reason whilst there is pressure still in the bottle it is not getting through to the low pressure side of the reg.
Has anyone else experienced this kind of problem, is the CO2 from a fire extinguisher of a lower quality than that supplied by the LFS and therefore causing problems with the regulator? Does anyone have experience of using FE's for a long time for this application, I would appreciate any info that can shed light on this problem -thanks