I was recently hired to migrate two WordPress websites from shared hosting to a VPS. These are types of job I do almost everyday. But one of the sites gave me bit of a trouble. A important page stopped working after the migration. There was no CSS loaded on that page. It was just few links with white background.

I soon realized that it was a page built with OptimizePress plugin. But still couldn't find what's wrong with it. Then I turned to server logs and found following,

Fatal error: Call to a member function generate_dialogs()

A quick Google search landed me on a OptimizePress help article which answered all my questions. They have a plugin dedicated to fixing this error. I installed the plugin and it was a quick fix from there.