What does "stuck" mean? Can you do anything else? Do it crash or just hang? Is there a crash/hang report?
Are all fonts OpenType with no embedding restrictions? Have you tried EPUB 3? Are you exporting to a local drive or a network drive?
When you state "convert", is this a print book that you are now exporting to Reflowable Text ePub, or have you set it up especially for this purpose as an ePub?
Things like page size and number of pages (and anything on a Master page) are irrelevant in this context.
What messages do you get when you try and validate the ePub: EPUB Validator (beta)
By the way, the fonts you want to use do not seem be available from Typekit which means you'll probably have to buy licenses to use them for an ePub.
Thanks for getting back to me on this. I managed to fix the issue. It was the Avenir text. Although I did buy the license for it, it gave me this issue. But once I changed it to a different version of Avenir, it went through perfectly and I got the EBook sent out and approved by the client.
So it was the font problem. Just changed it and the file got exported to ePub nicely.
Thanks again Derek and Bob!