Creating TFields in runtime

Hi:

I'm trying to create a TField in real time, but I can't, what I want to do
is the same task of Delphi's Field Editor, but I obtain an error message.
In the fields.zip file you can find the project where I'm working.

Thanks in advance.
begin 600 fields.zip
<uuencoded_portion_removed>
81DU02P4&``````8`!@!H`0``,0T`````
`
end