This seems to be a problem related to EZ Proxy as a result of off-campus authentication or using a laptop with WiFi on campus. It doesn't allow the frame to completely open once you log-in. EZ Proxy has not come up with a solution yet. In the meantime you can:
Go to the external PubMed site, sign in and search normally - you just won't have the automatic links to full-text articles that Walsh pays for. Ask a librarian for help getting full text of articles you need.
Use one of the library or lab computers on campus to search the Walsh PubMed database for full functionality.