20D Flash + Extension tubes

Hi Folks

I'm new to this forum - so I'll have to find my way around it - I like the comments I've seen so far. Now I wonder if someone out there could comment on one of my flash problems. The book seems a bit lacking in this respect although I have found some interesting articles on the web about it.

Question. How do I override the camera's decission not to fire if it can't find lock and the green light blinks? I know that the flashgun will give the correct exposure if I can override the system. I sometimes override by locking on the nearst bright object and moving the camera. That seems to get round the problem - but there must be a correct way in manual mode.

Question. Regarding the Kenko extension tubes mentioned - can anyone tell me if they will damage an EFs lens if used. And, where can I get them in the UK?
Will they be OK on a bog standard 18-55mm lens or the 28-200?

Jessopps have a set listed but claim not for the 300D - suppose this also applies to the 20D.

Regards

Have mode are you shooting in? When I have the flash on (550EX) or the flash up, mine always fires. I always shoot in the "creative zone", not any of the basic scene modes.

I'll let someone else comment on the extension tubes, I wouldn't like to give you incorrect information.

Well I have a set of jessops brought at Christmas that work with 300D no problem. What Jessops say is "Not compatible with EOS300" film camera.

I bought my extension tubes deom www.warehouseexpress.c​om - the Kenko set

Very nicely built considering the price

BUT! They will not fit the EF-S lenses. Nor will the Jessops ones as they are basically the same tubes (from what I have seen)

Buy the 50mm F1.8 and a set of tubes and you will be set