These messages are normally just notices generated by PHP when a variable value is read in the program and it hasnt previously been set. They do not affect the functionality of the plugin, or your website at any point. However they can cause the text to appear larger when they appear in the administration back end, and of course are unslightly in the front end of the website.
In most cases these messages should not appear. By default, hosts should set thier php configuration so that these messages do not appear. To do otherwise, can be a security risk, as it can expose information about your website to a potential hacker.
We are always working to try and eliminate instructions that generate these notices, so if you encounter one, then please let us know by posting a message on the forum
However, you can prevent these notices from appearing by adding the following code to your index.php in the root of your Joomla directory after the line: