See if creating the run time folder on a Windows 7 64bit machine makes any difference. The runtime files are "built" using some files from the currently installed copy of FileMaker so that might make a difference in the results. If not, they'll need to use windows compatibility mode or you'll need to upgrade fileMaker to a newer version.
Thanks for the quick reply!
That solution will be a bit problematic since I'd first have to get ahold of the client's machine, install my copy of FMP onto it, then generate every release from there. (This is a little pro-bono work I'm doing for a charity so I'm hoping I don't have to invest in new licenses just to help out. :-) )
I might have to switch to something else if we can't figure something out. It seems weird that there isn't just a "FileMaker Player" out there that would let one open the developed solution. (Doesn't it?)
If there are any other suggestions, that would be great!
I would borrow that machine and make that exact test. If it works, you have an answer. If it doesn't, your clients have to choose between XP compatibility mode, you getting a new version of FileMaker or using some other product.