There is a known bug about the Visor that sometimes you need to reset the Visor before it is able to sync properly. This is the number one solution for most people having problems syncing. If a soft reset does not work, and other USB devices work on this machine on Linux, a hard reset has been known to solve the problem. (Try some of the other suggestions before doing a hard reset).
Did you install the new kernel/modules?
Make sure that all the modules are running. The command is lsmod and there should be, at least, these modules: visor, usbserial, usbcore; and one of the following: usb-uhci or usb-ohci.
If you installed a new kernel, did you reboot?
Is the USB hardware enabled on your computer? (Check your BIOS. Does it work in other operating systems?)
Are things (ie "usb-serial") appearing in /proc/devices? In /proc/bus/usb/devices? If not, then the drivers aren't being loaded properly.
Is there any information being entered in syslog when you press the hotsync button?
Did you really remember to press the hotsync button BEFORE running your synchronization script?