So, I've found what my problem was.

There needs to be a file called KT_PATH.TXT in your Sketchup plugins folder. The contents of the file is just a one liner pointing at KERKYTHEA.EXE.

Mine reads (For Example): -

C:\Program Files (x86)\Kerkythea Rendering System\kerkythea.exe

I think that there may be an authority problem at installation time when it trys to write this file (Just a guess 'cause i haven't deleted it).

So maybe all you need to do is find where your KERKYTHEA.EXE is and create the above text file?

Give it a try.

My KT hasn't opened up 'automatically' since re-installing twice and upgrading PC once. I guess it is to do with the software not knowing the location of KT (may be SU may be SU2KT). I have been manually opening KT and then opening the .xml file created from SU2KT. I have Windows Vista Home Premium x64 so I thought that would be causing major probs with file locations etc (ie 'C:\Program Files' and 'C:\Program files X86' for starters). I will try to fix my installation and let you know the results.