I sent a message to this list a few weeks ago about this but I'm not 
sure that it was ever resolved.

xm save still fails on xen 3.4.2 when I try to save a domU running 
pv-ops 2.6.31.6 (domU & dom0 are 64-bit).

The original thread is here (contains log & config files):
http://lists.xensource.com/archives/html/xen-devel/2009-10/msg01477.html

If anyone can tell me whether this is a bug, or whether I'm doing 
something wrong, I'd really appreciate it.

Thanks,
Yasir