Title screens pixilating after exporting film? Please help

Hello, I'm a midwifery student so this is all very new to me...we just made a short film and used the 'titles' option to create black screens with white writing on...the film ran brilliantly on the mac, but now after exporting, every title page flickers from white to black, and then back and forth again. The visual film footage is fine, but the title screens in between are not good...can anyone help?
Can send the whole thing over on 'we transfer' if that's any help.
Many thanks good people in this community...you are my only hope
Best wishes,
Vicky
