Bad reception can cause all sorts of problems with mpeg decoders - its like a scratched dvd will sometimes lockup your dvd player but since its bad reception its random rather then the same point like on a dead dvd.
There have been some quality issues with the Zinwell boxes and there have been issues with boxes freezing up. The problem here is that it's also a very common issue occuring if you have poor signal strength. Without knowing your signal strength it's pretty hard to determine the issue but I'd suspect the problem lies with the aerial.
BER is the Bit Error Rate, which in turn relates directly to the Quality reading in the signal strength monitor page, this is found in the manual tuning area as previously mentioned. A good Quality reading is very important.
While the Zinwell/DSE boxs are not my choice of box, they in general operate as they should, if the Quality is good then they normally play ball. A poor input signal due to bad reception which can be due to poor antenna can cause issues you see, but as I have no comparison from your location who knows.
Personally, save your effort, get a proper UHF antenna installed and decided then if you have a problem with the STB, without a correctly engineered antenna you are simply wasting effort.