I opened a new document as suggested. Added a reference and chose the Env and Urban stlye. It gace the style with wrong format. But also then did not let me change my document properties (style) and kept giving me an error.

@pranabm1: Possibly you did not do the second trial in an empty document? This is a bug, but if you insert a single reference in an empty document, there should be no error (and I don't get one here). The best I could do was to trigger it with a combination of three references.

@dstillman, @adamsmith: There are some issues here. The preview on zotero.org/styles is also broken, and as far as I can tell it has been since the style was first released. (I ran a test over the style using the processor code in use when it was first checked in [January 2016], and it crashed there as well).

I've added a fix for the crashing error, but the style applies an odd disambiguation pattern that the processor cannot (and will not) handle. The pattern boils down to this:
<if position="subsequent">
<group delimiter=", ">
<text prefix="See reference " variable="first-reference-note-number"/>
<choose>
<if disambiguate="true">
<text macro="contributors-short"/>
</if>
</choose>
<choose>
<if disambiguate="true">
<text variable="title"/>
</if>
</choose>
</group>
</if>


The crash was triggered by the second disambiguate="true" conditional (for some reason that I haven't taken the trouble to pinpoint), but the underlying cause was the call to the contributors-short macro within the scope of the first condition. That call raises issues that I won't attempt to work around.

The processor applies disambiguation rules in sequence until a set of references either resolve or fail to disambiguate, as per the CSL Specification. The sequence is:

1. Show more names
2. Expand names (adding initials or full given names)
3. Add a year-suffix
4. Render the cite with the disambiguate attribute of cs:choose conditions testing “true”

The processor does not follow these rules precisely, but disambiguate conditions are applied after adding and expanding names. Therefore, at the stage where the disambiguate condition is triggered, there are no further name operations to be performed, and as a result, adding and expanding names beyond the baseline requirements of the et-al-min and et-al-use-first attributes will never occur in this style. It's a limitation of the CSL logic that actually makes pretty good sense.

While the style does need some form of disambiguation to function correctly, the style guide does not give any guidance on the rules that should be applied, so it looks like there should be leeway to just adjust the code of the style to avoid the chicken-and-egg problem described above.

That was just explaining why disambiguate-add-names is redundant there -- there isn't any havoc, it just won't do anything. I don't plan to make any changes apart from the crash fix.