To kill it in xterm:
Do "ps ax | grep vncviewer", remember the number at the beginning of the line displayed. Type "kill <number>". If that doesn't work, do "kill -9 <number>".

How are you connecting between the tablet and your PC?

Also, the free edition of VNC is fully functional, nag free, open source software, I assume you bought the personal edition? Why?
Try the free edition, it is possible that the additions in the protocol used by the personal edition is preventing you from connecting. The "One-Port HTTP & VNC" and "File Transfer" additions sound like they could case problems.