I just downloaded the trial and installed but when I attempt to log on I get this error:

Checking update program...
Connecting to update1.vendetta-online.com:21024...
Latest version: vendetta-1.8.218.1
Patching version vendetta-1.8.203 to vendetta-1.8.218.1...
Disconnected
Connecting to update2.vendetta-online.com:21024...
Latest version: vendetta-1.8.218.1
Patching version vendetta-1.8.203 to vendetta-1.8.218.1...
couldn't insert file index 0?
can't open update.rlb! aborting!

Update failed. Error code -99

Are you on a Mac? If so, you need to pull the vendetta app out of the VendettaOnline.dmg file, and stick it somewhere like applications folder, then run VO from there.

If not, I have no idea.

Same here!
I use kubuntu 12.04

Connecting to update1.vendetta-online.com:21024...
Latest version: vendetta-1.8.223.1
Patching version vendetta-1.8.203 to vendetta-1.8.223.1...
can't open update.rlb! aborting!

Did you install with sudo or otherwise as root? Because you're not supposed to. VO is supposed to be installed using your user account.