Gzip compression not working for one website but works for another one in the same Microsoft-IIS/7.0 server

Please help me to find the real cause.

A js file header from the website where gzip is not working

Request URL:http://www.gzipnotworkingsite.co.nz/UI/Page.js?v=1.16
Request Method:GET
Status Code:200 OK
Request Headers
Accept:*/*
Accept-Charset:ISO-8859-1,utf-8;q=0.7,*;q=0.3
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-GB,en-US;q=0.8,en;q=0.6
Cache-Control:no-cache
Cookie:__utma=xxx; __utmb=xxx; __utmc=xxx; __utmz=xxx.utmcsr=feedburner|utmccn=Feed:xxx|utmcmd=feed|utmcct=FaceBook
Host:www.gzipnotworkingsite.co.nz
Pragma:no-cache
Proxy-Connection:keep-alive
Referer:http://www.gzipnotworkingsite.co.nz/Home.aspx
User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.31 (KHTML, like Gecko) Chrome/26.0.1410.64 Safari/537.31
Query String Parameters
v:1.16
Response Headers
Cache-Control:max-age=2592000
Connection:keep-alive
Content-Length:7403
Content-Type:text/javascript
Date:Wed, 05 Jun 2013 01:24:03 GMT
ETag:"xxx:0"
Last-Modified:Fri, 15 Mar 2013 03:59:48 GMT
Proxy-Connection:keep-alive
Server:Microsoft-IIS/7.0
Via:1.1 SALMM1, 1.1 SALISA4
X-Powered-By:ASP.NET
X-WebMarshal-RequestID:xxx

A js file header from the website where gzip is working

Request URL:http://www.gzipworkingsite.com/UI/Page.js?v=1.16
Request Method:GET
Status Code:200 OK
Request Headers
Accept:*/*
Accept-Charset:ISO-8859-1,utf-8;q=0.7,*;q=0.3
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-GB,en-US;q=0.8,en;q=0.6
Cache-Control:no-cache
Connection:keep-alive
Cookie:__utma=xxx; __utmb=xxx; __utmc=xxx; __utmz=xxx.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none)
Host:www.gzipworkingsite.com
Pragma:no-cache
Referer:http://www.gzipworkingsite.com/Home.aspx
User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.31 (KHTML, like Gecko) Chrome/26.0.1410.64 Safari/537.31
Query String Parameters
v:1.16
Response Headers
Accept-Ranges:bytes
Content-Encoding:gzip
Content-Length:1225
Content-Type:text/javascript
Date:Wed, 05 Jun 2013 01:24:53 GMT
ETag:"xxx:0"
Last-Modified:Thu, 21 Mar 2013 23:22:38 GMT
Server:Microsoft-IIS/7.0
Vary:Accept-Encoding
X-Powered-By:ASP.NET