I see this problem all the time and the only way this will work correctly is if you have Acrobat Standard installed on the same computer. the reason that it is black is that the image is most likely a .png image and has built in transparency when placed on the title block. So what I do with my clients that have this drwg format is that I I convert the .png to .jpg and replace it - problem solved. You have a white background around the company logo (as opposed to the off-white of the the sheet background) but on PDF's you don't see the difference because the SW drwg background is omitted.
Thank you Mark, you nailed the problem.