Thanks for your response, turns out reinstalling TAC sorted it out...now before you clap your hand over your eyes and groan...I had thought I`d done this already but what I did do is cut the mod from Gamedata and paste it to the desktop, run KSP then paste it back. Must be corrupted in there somewhere. I do have a few mods installed which I suffer lag from e.g. GPP and G-OPP and all the pretties and I now face putting another 4gb module alongside the 12gb already installed. I`m pretty sure it`s needed as there is definite heavy hard drive activity after Kerbalising for a while. Anyhow, thanks again for your reply and I promise not to be such a plank in the future.