I've created my profile and ensured that the GMT time is correct. I've booked my time on the lab booking system but when the time comes and I click on the "Start Lab session" , I get the message Error: You do not have an active reservation. Can someone tell where I'm going wrong?
It can be a little confusing particularly if you're timezone is far from GMT. Try making a test booking to test things out and see if that works. Also, when making your booking, check all the times and dtaes carefully at each screen to make sure you are geting the slot you want. Take advatage of the confirmation email and check that, and after you've made your booking, check in the calendar to see if it is set for the date/time you expected. If you have to book for an inconvenient time don't worry as you can always cancel again.
There are a few more tips in this post also:
Let us know how you get on, and if you still have problems