Blank PDFs in X7 on Windows 10

I am on windows 10 with Coreldraw X7. I have a large file ( artwork for a banner ) 6m x 3m - I have tried everything to export/publish this to a pdf but keep getting blank pdf files. After searching on the forum I have tried converting everything to curves, updating my .net, both publishing and exporting. Nothing helps.  I am getting desperate as I am on a deadline for production.  Please can someone help me.  Thanks in anticipation (and desperation!!)