Is there a minimum Wordpress version for the Popup Plugin?

I am working on a Wordpress site for a nonprofit that is about to launch a month-long fundraising campaign. They have Popup installed. This is my first year helping with this campaign, but clearly they have used Popup for years and as recently as December. I am finding that I cannot open any of the popups in the system or create a new one. When I do I just see a black window. I thought maybe the problem is that their Wordpress version is quite out of date. 3.5. I intend to update that for them but not until the end of the month because I fear breaking their site during this important event. Anyway, can you tell me about the backwards compatibility of Popup. Is Popup Pro different?