Thanks for code. This helped me to find my mistake.

I had generate a check constraint (LTRIM(MYFIELD)<>'') on my table,
and forgot it. If I drop, insering works fine.

But how can I check this field similary to a string field?
(If I set this field to Not null user will be able to append a space
instead of important data. That is why I use LTRIM)

Thanks.

Sandor