As configured the autofs module for ext2 filesystems will
try to run e2fsck on the filesystem before mounting and
will refuse to mount the filesystem if e2fsck returns an
error code.

However, the current e2fsck (from e2fsprogs-1.12-2) returns
an error if run on write-protected device.  This means that
autofs will fail to mount write proteted floppies when
using a line line:
    ext2-floppy      -fstype=ext2      :/dev/fd0
but will quite happily do the right thing for:
    dos-floppy       -fstype=vfat      :/dev/fd0
or
    auto-floppy      -fstype=auto      :/dev/fd0
This last one, however is less than ideal because it fails
for DOS floppies and doesn't run fsck on ext2 floppies.

The fix would seem to be to check if the device is read-only
before invoking e2fsck, and using the -n option if it is.