> I cannot find anything new in my understanding regarding its relevance to
> the problem.

When you run your script in Development Studio or other tool,
transaction is committed after each DDL. When you run the script in
IBScript component it isn't. Mixing DDL and DML in one transaction
always lead to errors like yours.
BTW, why you do your conversion using temporary column? Why not
change type of the column immediate?

SY, SD.