Joomla 3.1.4 ,JInstaller: :Install: Cannot find Joomla XML setup file,error - plugins

Question

I have setup already joomla 3.1.4 and I tried to install a plugin,But Im getting this error:
JInstaller: :Install: Cannot find Joomla XML setup file
This is my xml file:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE install PUBLIC "-//Joomla! 1.5//DTD template 1.0//EN" "http://www.joomla.org/xml/dtd/1.5/template-install.dtd">
<extension version="3.1" type="plugin" group="content" client="myjoomlasite">
<name>plg_content_helloworld</name>
<author>Tahsin Çetin</author>
<creationDate>July 27th,2013</creationDate>
<copyright>Tahsin Çetin</copyright>
<licence>GNU General Public License</licence>
<authorEmail>tcetin#yandex.com</authorEmail>
<authorUrl>http://tahsincetin.com</authorUrl>
<version>1.1.0</version>
<description>Simple Hello World plugin</description>
<files>
<filename plugin="helloworld">helloworld.php</filename>
<filename>index.html</filename>
<filename>helloworld.xml</filename>
</files>
</extension>

Answer 1

You do not need to specify "helloworld.xml" in your xml file.Remove file and install again.This will be your final xml file-
<?xml version="1.0" encoding="UTF-8"?>
<extension version="3.1" type="plugin" group="content" client="myjoomlasite">
<name>plg_content_helloworld</name>
<author>Tahsin Çetin</author>
<creationDate>July 27th,2013</creationDate>
<copyright>Tahsin Çetin</copyright>
<licence>GNU General Public License</licence>
<authorEmail>tcetin#yandex.com</authorEmail>
<authorUrl>http://tahsincetin.com</authorUrl>
<version>1.1.0</version>
<description>Simple Hello World plugin</description>
<files>
<filename plugin="helloworld">helloworld.php</filename>
<filename>index.html</filename>
</files>
</extension>
Hope this will help.

Answer 2

The "Cannot find Joomla XML setup file" usually means you are trying to install an extension that wasn't designed for the version of Joomla you are installing to.
Read more here

Answer 3

In your opening <extension> tag, you do not need to specify a client attribute.
Where is the XML file in relation to your ZIP package? If it isn't at the top level of the ZIP, it won't be found.

Answer 4

Generally when this happens something is wrong with the XML file. If you have made any changes, try to think where those changes were and find a problem with the XML file.
Problems could be:
No opening or closing tag. Closing tags are easy to miss. Count them, make sure there's an opening and a closing tag.
Duplicated tags. It's easy to add two labels or showons for example, especially if you are copying and pasting.
Space before the opening XML tag
No closing fieldset tag
No closing extension or config tag. Easily deleted if you are replacing the file
You can easily use a tool like this:
https://www.w3schools.com/xml/xml_validator.asp
Which will help you to find issues such as missing opening and closing tags.