after I burn the 1st DVD I insert another DVD into my drive and click on burn (again) it goes thru a moment or two then says I need to insert a blank disc
If you are trying to burn the second DVD by clicking burn (1) in the image, I do not think this is possible as MEP has already determined the disc type and size for the first burn and does not re-detect the new disc.
Close the Burn window 2 in the image, then restart the Burn process again - 3 in the image - MEP will then recognise the new disc. (it is a bit of a pain to do this ).