When I mount using the loop option of mount:

[root@moebius rh70img_reiser]# mount -tiso9660 -o loop -oro \
7.0-Reiser-i386-disc1.iso /mnt/loop 

I get :

ioctl: LOOP_SET_FD: Invalid argument

in an other bugzilla-report there was given advice to do:

mount -tiso9660 -oro 7.0-Reiser-i386-disc1.iso /mnt/loop

this gives me: mount: 7.0-Reiser-i386-disc1.iso is not a block device
(maybe try `-o loop'?)

.. I tried it with many images, all working as soon as burned on a cdrom

I use an Athlon system with red hat 7.0, updating with all (10th Dez.2000)
available update-packages did not change the problem.

A friend of mine said that he has the same problem (red hat 7.0 without
updates, older hardware)