Lines disappear when I export my map

[SaraBowers]

I created a map and exported it to PDF, but it looks different in PDF than in layout view. One of my layers is an outline of the US, and portions of the boundaries disappeared when I exported the map. I don't have any shapefiles on top of my states layer that should be blocking the lines; only geocoded points. Does anyone know what I might be able to do to fix this and make my lines appear properly?

[HollySmith]

I have this same problem when exporting to pdf. Some lines appear, but others disappear. They have been exported as in the thumbnail preview panel in the pdf, the lines are there! They just don't show in the large page... very strange. I am using data driven pages, does that make any difference?

Any one have any ideas?

[HollySmith]

I have just worked out how to solve this! Change the transparency to 1% and the lines export correctly! So strange ArcMap...