I am getting this error message while doing text search (Search due to its high frequency and low importance ).
IR Expert starts to exlude words from relevance searches if they occur in too many documents for the search to return helpful information.
The main instance where I see this happen is during demo/testing where a ton of tickets are entered with the word "test" and . It they demonstrate IR search by searching for "test": it stops working after a while becuase too many documents include the term to allow for relvance ranking--too many records match for it to be helpful. (Stop words are defined words to ignore when performing a query and normally include very common terms such as "the". "and", etc.)