No, you'll need to update both client and server to 4.9. I highly recommend this.
In the meantime, as a workaround, you should be able to resolve your update issue with the following:
* check for modified files in the workspace, Keep any that there are
* run "accurev update -9"
* from the root dir of your workspace, run "accurev pop -O -R ."
You should then be in a consistent state. If that doesn't work for you, I'd suggest you open a Support case with our team.