Following is a list of most commonly occurring Joomla error messages, with instructions on how to set these.
Fatal error: Call to undefined method RuntimeException::get().
This error normally comes, when you try to upgrade joomla from 2.5 to 3. The major reason for this cause is may be in your non native system plugin with onAfterInitialise method.
Fatal error: Call to undefined method stdClass::onDisplay()
This error occurs with the creating new content option. Uploading fresh files could resolve the problem.
Fatal error: Call to undefined method JModel::addIncludePath()
Extending your model class through JModelLegacy could solve the problem.
Fatal error: Call to undefined function utf8_ireplace()
Please navigate to /libraries/phputf8/str_ireplace.php and replace this file with a new new file.
Fatal error: Call to undefined method JControllerLegacy::get
To resolve this problem, download thhe appropriate joomla version, which you are using on your site. After that, extract the folders, “libraries” and “includes” and upload these to replace the two same folders on your site.
Call to undefined method JHtml::getJSObject()
Here is a very good post, describing the solution to this problem in a great detail. http://forum.joomla.org/viewtopic.php?f=625&t=691030
Fatal error: Call to undefined function apc_cache_info()
You can correct this error by setting cache handler to file from your Global Configuration Manager.
Fatal error: Call to undefined function jimport() in /public_html/includes/framework.php
To resolve this problem, download the appropriate joomla version, which you are using on your site. After that, extract the folder “includes” and upload this to replace the two same folders on your site.
Fatal error: Call to undefined method JRegistry::getValue()
JRegistry::getValue() has been changed and now in Joomla 3.x, you have to use, JRegistry::get()
While updating to Joomla 3 website. This has been observed mainly on the sites that are updated from Joomla 3.5 to higher versions such as Joomla 3.6.
Since Joomla 3.6 is out, we have been updating our websites to keep up-to-date. It is highly recommended that you always take a backup of your site before making any kind of changes on your website.
Especially when you are installing version updates for any major changes have deployed, it is highly recommended that you take a full backup of your website.
Here are the quick steps you should consider to fix this problem:
Log into the Administrator
Go to “Global Configuration”
In the “System” tab, look for the “Cache Settings” section.
Change “Cache” to “ON – Progressive caching”
Change “Cache Handler” to “File”
While this is not yet fully detected as to why it is happening we hope that this will be completely fixed in the future versions of Joomla.