A couple of people have been having problems with dumped ROM files coming out corrupt. Turns out this is a known problem, if you are interested in the gory details, check out this site.
For those of you who just want it to work, I’ve taken the code from the above site and ported it to C, to make a simple TI-85 ROM fixer. In order to use it, you must know your own ROM version first.
Make sure to read the included README file!