Huh. That's odd, because Dropbox is supposed to be able to open tiff files...
Did you try e-mailing the file to Dropbox and then go to it from within the Dropbox app? Maybe that'll work, instead.
There are also a bunch of apps that supposedly read tiff files. Although I don't know if any of these will work (I've never dealt with tiff files), I've read that Documents To Go opens tiff files. Or maybe Goodreader? I'm just throwing names out there - a Google search shows a bunch more.
Maybe the iPad just needs you to either restart or reset it? Sometimes, that's all it takes to get things "behaving" better...
Maybe some of this will give you some ideas. Sorry I'm not more help.
Marilyn