PS16 Ultimate - Windows 10

Have been trying to sort this out all week but have failed. I did a 46minute video which looked good in the Disc Simulator, so I burned it to DVD.

However on DVD playback there were a number of 5 second black gaps, especially but not exclusively amongst a group of stills I added as a slideshow with a music track under the slides. I had manually added transitions out (as I generally do), to the slides, So,  I replaced those transitions with the menu'd -transition out-disolve CPU and this seems to have cured black gaps the on the slideshow and other few areas. Full of optimism, I burned yet another DVD in the Export Tab but have found  that there are new black gaps ie which were not there before. Before fading to black on the DVD,  the transition starts to  let the  next clip show through but then goes black  for the rest of that clip..

I have expanded the time line to its maximum and can't see anything, and running the Disc Simulator there are no black gaps.  I'm just at a loss.

Any ideas anyone - please 

Thought I might try an export to file. Got part way through then it stopped with an Error Message as follows

WARNING

The Export process has experienced problem with the timeline and has been cancelled

(Ox E000005)  40949 / 69314 @ 00:27:17:24 [00:00:00:00:00:46:12:14] 

I am guessing, but could be wrong that it stopped at 27mins  17 secs  24 frames.  Had a look there and its in the middle of a clip, no cuts, or effects etc.  Haven't a clue what the rest of the message means.