Somebody will have trouble with even the greatest and bestest and most intuitable interface, guaranteed. These experts are much too close to the project to correctly orient themselves from the perspective of either a beginner or a goals and tasks driven end user. Any attempt to construct the single best method to complete any task and achieve any goal is unlikely to succeed because end users are not all alike. End user baggage ranges from unfamiliarity with computers to unfamiliarity with the web to unfamiliarity with the concept domain. End users are not stupid, but they can come from a bunch of very weird places.
People are different.
People possess a wide range of attitudes towards, well, everything. So, provide multiple solutions to any problem, multiple tools for any task. Provide separate interfaces for simple search and advanced search. Don't focus so much on restrictive field searches. Allow for searches and index or table of contents browsing.