> From what I can see, this is an excellent case of detecting the

wrong param

> datatype due to an old Firebird error.

I found the solution to this problem in this article. You were right,
it's an old Firebird error and the problem is solved in IBO v 4.3 but
I have IBO v4.
Anyway, the solution is here:
http://www.ibobjects.com/iboNews.html#fb153client

Thanks for your help.