Are you running UBCD from an USB stick?
Avira won't work in that cas because it can't find its antivirus definitions. It is a know bug of the Avira Rescue CD. It should be fixed in the next update of the Avira Rescue CD, but it takes a very long time before they update their CD.
Post your exact problem at:
Download Ultimate Boot CD v5.0
Use Parted Magic
for handling all partitioning task: http://partedmagic.com/