exactly the same problem, I mailed in my check. here's the message I got from them after i emailed them the problem:
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If you were not able to proceed to the next portion of the secondary application after clicking the "Continue" button, please go to one of the following web sites to finish your application.
To pay on-line, go to:
https://www.applyweb.com/public/register?s=osupm. Once you click "Continue", you should see another section of the application with additional questions. At the end of this section at the very bottom of the form there is a 'button' labeled 'Submit and Pay'. When you click on "Submit and Pay", you should be able to enter your credit card information. Please let us know if this does not work.
To pay by check or money order, go to:
https://admissions.osu.edu/medicine/
We look forward to receiving your application materials. Thank you for your interest in The Ohio State University College of Medicine and Public Health.