Syslinux - Aug 2016 - lpxelinux hangs on R610 with recent BIOS, works with old BIOS

Decided to try out lpxelinux on a couple of Dell R610s.  Both versions 5.10
and 6.03 hung on a server with fairly up-to-date BIOS (6.1.0), but work
fine on another R610 with old BIOS (1.2.6).

Watching the TFTP log and running tcpdump on the PXE server, I see it
download pxelinux.0 (renamed from lpxelinux.0), but it never even tries to
transfer anything after that succeeds.  It eventually (seems like minutes)
announces that it can't find ldlinux.c32 though the compatible version is
there.

Some additional details

Failing system has:
Broadcom boot agent v6.0.11

Successful system has:
Broadcom boot agent v5.0.5

both claim base code is v1.1.1

Anything I can do to help debug this?
I'm in a position to upgrade the BIOS on the machine which is succeeding
and/or to capture traffic when it boots.  Not so easy to do that with the
machine with the newer BIOS though.

Thanks, Scott

> Decided to try out lpxelinux on a couple of Dell R610s.  Both versions 5.10
> and 6.03 hung on a server with fairly up-to-date BIOS (6.1.0), but work
> fine on another R610 with old BIOS (1.2.6).
Considering that there are newer versions than 6.1.0, and that they 
probably include updates to the PXE ROM, there might be some relevant 
issues in the specific "BIOS" v.6.1.0. Whether it is worth the update 
from 6.1.0 and test again, I have no idea.
> 
> Watching the TFTP log and running tcpdump on the PXE server, I see it
> download pxelinux.0 (renamed from lpxelinux.0), but it never even tries to
> transfer anything after that succeeds.  It eventually (seems like minutes)
> announces that it can't find ldlinux.c32 though the compatible version
is
> there.
> 
> Some additional details
> 
> Failing system has:
> Broadcom boot agent v6.0.11
> 
> Successful system has:
> Broadcom boot agent v5.0.5
> 
> both claim base code is v1.1.1
> 
> Anything I can do to help debug this?
> I'm in a position to upgrade the BIOS on the machine which is
succeeding
> and/or to capture traffic when it boots.  Not so easy to do that with the
> machine with the newer BIOS though.
> 
> Thanks, Scott
Regards,
Ady.