AddOn not working and cannot be removed

As for the error for the addon
All the addon files are located under /etc/frontview/addons NOT /frontview/ui/resource/html/COOLADDON
/var/run/COOLADDON.pid
/etc/frontview/apache/addons/COOLADDON.conf
/etc/frontview/addons/ui/COOLADDON
/etc/frontview/addons/ui/COOLADDON/COOLADDON_HANDLER.pl
/etc/frontview/addons/ui/COOLADDON/COOLADDON.js
/etc/frontview/addons/ui/COOLADDON/COOLADDON.html
/etc/frontview/addons/ui/COOLADDON/language
/etc/frontview/addons/ui/COOLADDON/language/ja
/etc/frontview/addons/ui/COOLADDON/language/ja/COOLADDON.str
/etc/frontview/addons/ui/COOLADDON/language/zh-tw
/etc/frontview/addons/ui/COOLADDON/language/zh-tw/COOLADDON.str
/etc/frontview/addons/ui/COOLADDON/language/en-us
/etc/frontview/addons/ui/COOLADDON/language/en-us/COOLADDON.str
/etc/frontview/addons/ui/COOLADDON/language/de
/etc/frontview/addons/ui/COOLADDON/language/de/COOLADDON.str
/etc/frontview/addons/ui/COOLADDON/language/fr
/etc/frontview/addons/ui/COOLADDON/language/fr/COOLADDON.str
/etc/frontview/addons/ui/COOLADDON/language/zh-cn
/etc/frontview/addons/ui/COOLADDON/language/zh-cn/COOLADDON.str
/etc/frontview/addons/ui/COOLADDON/language/ko
/etc/frontview/addons/ui/COOLADDON/language/ko/COOLADDON.str
/etc/frontview/addons/ui/COOLADDON/COOLADDON.xml
/etc/frontview/addons/bin/COOLADDON
/etc/frontview/addons/bin/COOLADDON/running.sh
/etc/frontview/addons/bin/COOLADDON/start.sh
/etc/frontview/addons/bin/COOLADDON/stop.sh
/etc/frontview/addons/bin/COOLADDON/COOLADDON_service
/etc/frontview/addons/COOLADDON.remove

The errors I posted above are bugs in the following files:

For the image errors
/frontview/dashboard/index.html
/frontview/dashboard/dashboard.html
/frontview/dashboard/wizard.html

For the install errors
/frontview/dashboard/legacy/addons/installed/installed.html
/opt/installed/installed.html

Okay I have found some problems in the SDK located http://www.readynas.com/download/addons/addons_sdk.tgz that was causing it not to work.

addons_sdk\template\ADDON.xml
-----------------------------------------
<get_url>/addons/%ADDON%_HANDLER.pl</get_url>
<set_url>/addons/%ADDON%_HANDLER.pl</set_url>
should be changed to
<get_url>%ADDON%_HANDLER.pl</get_url>
<set_url>%ADDON%_HANDLER.pl</set_url>

addons_sdk\addon.config
-------------------------------
RESTART_APACHE="n"
should be changed to
RESTART_APACHE="y"

There is one more issue where it does not save the runtime seconds into /etc/default/services file.
I will look into that tomorrow.

You may find the SDK here useful: https://gitorious.org/readynas/frontview-sdk

Thanks, that works.
This SDK uses
<get_url>../addons/%ADDON%/%ADDON%_HANDLER.pl</get_url>
<set_url>../addons/%ADDON%/%ADDON%_HANDLER.pl</set_url>
which works and you don't need to restart apache.

Funny though that the photo addon that is included with the readnas uses %ADDON%_HANDLER.pl and even the third party HTOP does as well.

For some reason this SDK has commented out the code that has the "run time seconds" setting.

The "run time seconds" value isn't needed. It's just part of the example add-on.