FIELD IS NOT A BLOB ERROR

Greetings,

HELP HELP HELP

We are getting a 'FIELD IS NOT A BLOB ERROR' when writing to a paradox 7
table
from inside a Delphi 2 application.
This is the scenario :

The routine that writes to the TTable component is as following:

Table1.cachedupdate := True;
with Table1 do
  begin
  Insert;
  FieldByName('Trx').AsInteger := 12345;
  FieldByName('ExtraInfo').SetData( nil );      (* This is a Blob field *)
  post;
  End;
Table1.ApplyUpdates;

This causes the above named error.
However if i don't use the cachedupdate method, it runs happily.

Why does turning cached updating on cause this error ???
What is the correct full proof way of writing a BLOB to a Database TABLE???

Thanks in advance.

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