The short answer is that my reading of the regulations is that you can still obtain your Master's (assuming you've passed every else), but that you can't earn a merit or distinction. The long answer is below...
The quotes below are all from
Regulation 9 Postgraduate Taught Awards on their web site.
You've said that "total credits are 180 my all modules are passed", but the regulations say that those 180 credits "will normally include a dissertation".
Can you confirm how many credits the dissertation is worth, and whether it represents some of those 180 credits or is in addition to them? (Your first post says, "its credit is zero", which implies that it does not contribute to those 180 credits and has no impact on your final award. I'd just like to double-check.)
This is important as paragraph 10.8 provides details of the minimum mark required in "in individual modules amounting to 160 Credits" and in "individual modules amounting to the other 20 Credits".
If the dissertation is in
addition to the 180 credits then its capped mark of zero will
not impact "the award of the Degree of Master". It
will, however, impact the ability for you to be awarded "with Distinction" or "with Merit".
It would obviously be better for someone at the university to confirm the above, rather some random stranger on TSR (me).