Not only do we have to contend with the dreaded 'not provided' listing in Google Analytics for organic searches where customers were logged-in to their Google accounts, but we also have the 'Not Set' issue to contend with.
So what exactly is 'not set'? It is a placeholder for any information that has not been received for the Dimension you have set.
'Not set' can be seen for the Advertising Dimensions of campaign, ad group, keyword, match type. It can also be seen for Landing Page listings and Visitors flash version, screen colours and language.
For Landing Pages, 'not set' means that there is no _trackPageview code on the page so Google is not able to identify the landing page that was used.
For Technology, Browser & OS and Screen Resolutions, 'not set' can be seen for flash if it is disabled in browser settings, screen colours and language.
For Adwords, 'not set' means there is an issue with your account linking, like a url redirect, incorrectly tagged urls or missing data in Adwords Reports. It can also eventuate from Display Network traffic as there is no keyword search associated with these ads or can be because of invalid clicks.
For Custom Reports and Visitors Flow, 'not set' is used to clarify any visits that were not attributed to campaign sources.
For Search Keywords, 'not set' means that visitors did not land on your page using search (via a keyword), they may have come directly to your site or by a referral link or Google Maps.
In essence, 'not set' can be useful to show you where there are issues in your tracking code or is used when the Dimension you are looking at has no keyword associated with visitors being referred or linking to your site.
If you are having issues with 'not set' for your Landing Pages or Adwords, contact us so we can diagnose what could be causing the error.