Autoincrement Bytes.
I was happily coding up an example where I have a ADO.NET 1.x DataTable that's has an auto-incrementing field. Being the conservative type I am, I had coded the two fields to be of type Byte. When trying to create the ForeignKeyConstraint related to that column, I got an exception:
Property not accessible because 'Parent Columns and Child Columns don't have type-matching columns.'.
Sure enough, if you go check the DataType of the auto-incrementing column, its been "upgraded" to System.Int32. Silently. Nice. Now that you know the problem, the fix is easy. Make the columns Int32's. Ick.
Leason learned after 20 minutes of chasing that one down. Its going to be a grrrreeeaaat week.