<i>Could this be caused by the untivirus being uninstalled?</i>
Yes, it could. Some shared library (used by the backup software) could have been removed when the antivirus was uninstalled.
How to install the antivirus software could depend on the specific product and version you are using, and it could probably be done from a central management console on an antivirus server, or just running the installer on the client box.
Some clarification could be needed, since you metioned that the backup management console was uninstalled first, but then you asked about an antivirus uninstallation.