Virus ti2 after a complicated patch just freeze on one tone, please help

[MBTC]

It may not be your Virus at all... it can be anything from a MIDI loop to your DAW, USB issues, etc. Start by process of elimination... There are a lot of folks in the purely analog world who refuse to use USB on synths even for MIDI, because they insist it is the root cause of most things getting screwed up. If needed try MIDI + plain audio cables to your interface. Depending on what DAW you use, make sure you've properly got the hang of utilizing external hardware with it.
A lot of folks new to hardware synths (not saying you are, but just in case) are surprised to find there's a whole world of new stuff to learn in order to keep things running smoothly, but in the end its worth it for the difference in sound.

The only way to troubleshoot sometimes is to make sure you understand all of the points that can be changed. Change one at a time and see if it makes a difference. Repeat until you've found the culprit.