If you are trying to deploy from a server to a client, you might run into the same thing I did.
I had the same issue... and after trying the above replies, still had the problem. Then I found this:
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2009110411364348
Turns out by recreating the deployment install pack not as a single EXE, then copying the two live update files it mentions from the CD over the ones in the deployment files... the deployment worked first try. Just had to point the deployment software in one more folder for it to recognize as a valid package to deploy.
Kind of lame that the live update files in the deployment packs made in RU5 aren't the latest ones needed for Windows 7... when they come on the same CD I used to install the software to begin with... but at least it works now.