I am unable to open the Appian 7.4 designer even after successful installation a

There are no issues at all, that message is a false positive. This seems more of a problem on how or from where you are hitting the URL rather than an issue with your installation.

1. Can you try with other browser? (e.g. Chrome)
2. Check your network settings on IE, it could be you are using a proxy which may not be allowing you to access this URL. To find out go to Internet Options - Connections - LAN Settings

3. Download Jing www.techsmith.com/.../ and record the ENTIRE screen when performing these steps:
---> 3.1 Stop JBoss
---> 3.2 Start JBoss
---> 3.3 Try accessing the same URLs so the attempts get recorded in the video. Make sure you record the whole screen and not only the browser, I want to see where JBoss is running in the background while you test on IE

http://127.0.0.1:8080/suite
lp-3c970e26ff39:8080/suite
http://localhost:8080/suite
http://localhost:8080/suite
http://lp-3c970e26ff39:8080
http://localhost:8080

--->3.4 Attach the SWF recording.

There are no issues at all, that message is a false positive. This seems more of a problem on how or from where you are hitting the URL rather than an issue with your installation.

1. Can you try with other browser? (e.g. Chrome)
2. Check your network settings on IE, it could be you are using a proxy which may not be allowing you to access this URL. To find out go to Internet Options - Connections - LAN Settings

3. Download Jing www.techsmith.com/.../ and record the ENTIRE screen when performing these steps:
---> 3.1 Stop JBoss
---> 3.2 Start JBoss
---> 3.3 Try accessing the same URLs so the attempts get recorded in the video. Make sure you record the whole screen and not only the browser, I want to see where JBoss is running in the background while you test on IE

http://127.0.0.1:8080/suite
lp-3c970e26ff39:8080/suite
http://localhost:8080/suite
http://localhost:8080/suite
http://lp-3c970e26ff39:8080
http://localhost:8080

--->3.4 Attach the SWF recording.