Thanks for your reply Igor.
The images could possible be a bit large at 5184 x 3456 pixels but I have used similar sizes before with no problems.
I have upgraded to 9.0.10 but the out of memory issue is still there.
The show I am having problems with is built as follows: 5 x 10 portrait styles at the beginning of the show, followed by a series of individual images, then 2 x 10 portraits styles at the end.
I have experimented with removing the 10 portraits slide styles from the beginning and reverting to basic single images, but leaving the two at the end. The HD video creation then works fine until it reaches the last image of first 10 portrait styles at the end. it then freezes .
Could the issue be with the 10 portraits style?