We've been using an Access Database to front a SQL Server database. It's handy in that we can leverage all the simple UI features that Access Provides, such as drop-down lists.
However, recently we had a problem when we couldn't update any rows and we were getting this mysterious "Write Conflict" error.
Turns out that Access UI tries to assign default values to columns, and for some data-types, this causes problems.
Here's the MS Knowledge base article: You may receive write conflict errors when you update records of a linked SQL Server table in Access 2000