Access is creating Null bit fields, which causes a type mismatch.
or
The linked table is using fields defined as floating point data type (i.e. Real). This data type allows for storing "floating point" number data. When the edited record is passed to SQL Server, if both engines see the data in these fields as having the identical value, there is no problem. However, because of the "rounding" algorithms used by JET and SQL Server, the actual value compared may be different. Since JET has to review each field and see if there are any concurrency issues, when JET compares the number it sees (in the "Real" data type field) to that value stored in SQL Server, if it does not match exactly the record is assumed to have been changed and a Write Conflict occurs.