Not sure how you can start a new topic but not reply.

All I can suggest is clear cookies and/or reboot your computer.

You obviously have no problem posting, so not sure why you are unable to reply. 

Try again here.

I sometimes have the same problem - but only when using IE....try firefox or another browser maybe

Yay ,thank-you works on Firefox

For future reference, if others find they can't post - I think the forums have flood control, so if you're trying to reply to too many topics too quickly, you'll click reply and nothing will happen. You need to wait a minute and you'll be able to respond.