What's up with yum lately

[Douglas Phillipson]

For the past couple of months, yum seems a bit flaky.  Running FC4 some 
of the repositories are unavailable and yum just fails and dies.  Are 
there any parameters I can set in my xxxx.repo files or yum.conf that 
will allow yum to continue if a repository is down?  If a particular 
repository is down, I still want to update anything from repositories 
that are up.

I'm also getting the following error:

Setting up Update Process
Setting up repositories
Reading repository metadata in from local files
primary.xml.gz            100% |=========================| 861 kB    00:03
http://ftp.belnet.be/packages/dries.ulyssis.org/fedora/linux/4/i386/dries/RPMS/repodata/primary.xml.gz: 
[Errno -1] Metadata file does not match checksum
Trying other mirror.
Error: failure: repodata/primary.xml.gz from dries: [Errno 256] No more 
mirrors to try.

Does this indicate someone is trying to spoof a repository?

Thanks

Doug P