Recently we hit a strange problem on a VB.NET 2005 application. Stripped down to its bare essentials the code was as follows:

Dim connectionString As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\LinkCheck\db.mdb"
Dim sql As String
Dim adapter As OleDbDataAdapter
Dim cmdBuilder As OleDbCommandBuilder
Dim dsLinks As New DataSet
Dim rowcount As Integer

sql = "SELECT * FROM [Link] WHERE [IncludeInSearch] = True"
adapter = New OleDbDataAdapter(sql, connectionString)
cmdBuilder = New OleDbCommandBuilder(adapter)
adapter.Fill(dsLinks, "Link")

With dsLinks.Tables("Link")
  For rowcount = 0 To .Rows.Count - 1
    .Rows(rowcount).Item("IsIndexed") = "yes"
  adapter.Update(dsLinks, "Link")
  Next
End With

The Update command failed with "Syntax error (missing operator) in query expression". Now in this scenario that update command is built automatically by OleDbCommandBuilder. My immediate thought was that there was a conflict between some of the field names and Access reserved words. I changed any that looked to be possible candidates, but the problem remained.

After further research I discovered and added the following two lines:
cmdBuilder.QuotePrefix = "["
cmdBuilder.QuoteSuffix = "]"
These set the beginning and ending character to use when specifying database objects whose names contain characters such as spaces or reserved tokens. This resolved the problem.