Access Shared Database

We have a database that is shared on a network. It is set to be shared, but we continue to get the following error at different times.

“The database has been placed in a state by user “Admin” that prevents it from being opened or locked.”

We have that person close and then mutiple people can open.
What can we do so multiple people can have this open and continue to work. The database contains 4 simple tables, a form and a report that runs off a parameter query.