yum errors on unsigned package and on --exclude

[Kim Lux]

I am trying to update my FC3rc3 installation using yum.

I've done a yum install yum.

Everything appears to work OK until I receive this error:

<snip>

  Update: python.i386 0:2.3.4-11
  Update: python-devel.i386 0:2.3.4-11
  Update: system-config-packages.noarch 0:1.2.20-1
  Update: up2date.i386 0:4.3.47-5
  Update: up2date-gnome.i386 0:4.3.47-5
  Update: xinitrc.noarch 0:4.0.14-1
Is this ok [y/N]: y
Downloading Packages:
unsigned
package //var/cache/yum/development/packages/gthumb-2.4.2-4.i386.rpm

<end of snip>

So then I try to exclude it from the update and because it doesn't find
a match for it, it won't proceed with the update:

<snip>
Could not find update match for --exclude=gthumb-2.4.2-2
No Packages marked for Update/Obsoletion

<End of snip>


"Packages" I've tried:

gthumb
gthumb-2.4.2-2
gthumb-2.4.2-4
gthumb-2.4.2-4.i386
gthumb-2.4.2-i386.rpm

up2date has a similar sort of problem in that it will error out because
one package isn't signed.  

How do I get my update done ?  What am I missing about using --exclude ?

Thanks