Sounds like there are quite a few people out there having/had similar experiences with fellshoes exasterbating problems around the achilles/heel area.

The link provided by Stan seems to describe my symptoms almost exactly well. I am begining to form the opinion that recent training has caused the 'retrocalcaneal bursa' to swell and this swolen condition is irritated further by the fellshoes which provide a much tighter grip around the heel area. The end result is quite painful if the shoes are worn for sometime.

Although I tried running yesterday (in road shoes), I only managed 400m before I decided that things weren't quite right. However my particular ailment seems to be responding well to ibuprofen gel and I reckon that I will be OK to try again tomorrow.

I also think I will be able to wear my fellshoes again if the bursitis has completely cleared, but in the mean time I am sticking to roadies. I may invest in a pair of off-roaders that have been derived from a road running background as a back up pair - those Mizunos look promising.