"Operation not applicable" exception

Here is what I am trying to do:

I have a table with few fields.  Programmatically I am adding
few more to it and also adding some data.

Now, When I try to set properties like IndexName, I get a
'Operation not applicable' EDBEngine Exception.  Funny
thing is that if I handle the exception and repeat the same
statement it seems to work.

The same problem is happening with GetFieldNames function.

Any one knows whats going on, what might be causing the exception.

Thanks.  Please send a personal reply also.

Hemant