FWIW I've gotten that message too - doing a bit of digging...it seems 
that the TTCFont only handles fonts with subfamily names
'Bold' 'Italic' 'Bold Italic'.  Anything else it considers an error.  
The method in question is TTCFont>>derivativeFont:

The Vera fonts have subfamily names like 'Roman' or 'Oblique' which 
freaks out TTCFont.
In fact, the base font seems to have a subfamily name 'Roman' but the 
TTCFont assumes the base font subfamily name is 'Regular'.

So, what happens is the first font loads in OK because no analysis is 
done on the subfamily name.  The second font causes a reorganization of 
the family name cluster and you get all kinds of assumptions being 
broken by unexpected subfamily names.  So you can never load in a 
second Vera font.

I think the solutions would include:  naming the base vera font 
subfamily name to 'Regular' or changing the isRegular implementation to 
conclude 'Roman' also implies a base font.  Plus eliminating the 
subfamily name assumption in TTCFont (why not use a dictionary?).

But until this is sorted out, the Vera's aren't too usable with the 
current TT lib.

On Tuesday, June 24, 2003, at 04:50  AM, Jim.Gettys at hp.com wrote:

> Yes, you can redistribute Vera freely.
>
> If you modify them, please let us know.  The license requires you 
> change
> their name if you do so; but similarly, we have a contract with 
> Bitstream
> to get changes upstream to the fonts (so long as the quality is 
> maintained).
> They (and us, the Gnome foundation) must approve any changes to the 
> fonts if
> they retain the Bitstream name.
>
> I don't understand the message you are getting....  This hasn't been 
> true
> to my knowledge from anyone else using the fonts (at this point, they
> are in widespread use, both using Xft rendering technology and other
> rendering technology (e.g. OpenOffice, which uses Freetype, but not the
> other stuff that Xft does).
>                             - Jim
> --
> Jim Gettys
> Cambridge Research Laboratory
> HP Labs, Hewlett-Packard Company
> Jim.Gettys at hp.com
>