which chdman are you using? the one built with the current source (u5) will convert the discs fine (even the dumps are currently bad, and the chd has to be recreated from raw gdi files) the one built with u1-u2 source won't handle properly the gdroms
anyway, you can safely convert all chds but the laserdiscs to v5 at this point. the worst that can happen is that some disc make chdman to freeze but it seems to be happening at random (and only on windows) so it's not really easy to debug the problem