A family of Microsoft relational database management systems designed for ease of use.
A multiuser database should - I'd say for 2007 and later versions must - be "Split" into a Backend (containing just the tables) and a Frontend, containing links to the tables along with all the queries, forms, reports and code. A2010 requires that the user have exclusive access to the database if they are doing ANYTHING involving VBA code (opening a code-bearing form or report in design view, for example). Or of course the user on FrontDesk may be opening the database exclusively.
Split your database (using the Database Splitter Wizard) and give each user a copy of the frontend on their own C: drive. This will prevent both this error and the much more serious risk of bloating and corruption of the shared database.