Access database: could not save; currently locked by another user

Our multiple user program use C# for front end and access database for back end. Access database only has tables. Frequently, access database give error messages "could not save; currently locked by another user" even when only user was using the database. I am looking for an experienced Access and C# programmer to help resolve this issue.

[Error Message]: Could not save; currently locked by another user.
at System.Data.OleDb.OleDbCommand.ExecuteCommandTextErrorHandling(OleDbHResult hr)
at System.Data.OleDb.OleDbCommand.ExecuteCommandTextForSingleResult(tagDBPARAMS dbParams, Object& executeResult)
at System.Data.OleDb.OleDbCommand.ExecuteCommandText(Object& executeResult)
at System.Data.OleDb.OleDbCommand.ExecuteCommand(CommandBehavior behavior, Object& executeResult)
at System.Data.OleDb.OleDbCommand.ExecuteReaderInternal(CommandBehavior behavior, String method)
at System.Data.OleDb.OleDbCommand.ExecuteNonQuery()
at EZChart.FormPatients.AddStatus(String StatusType)