Success! I recreated the material from scratch. For anyone having the same issue, I edited the texture image, changing it from 300x300 pixels to 512x512, and I saved it under a new name. I then rebuilt the material using the new name also. It has started rendering again.

Now if I could just solve the issue of the model's geometry not caching. That was the reason I did the 'select all+copy+paste-in-new+save-as-new' trick last night. It has not helped. I may head over to the Podium official forum and see if I can get some ideas.

Thank you again, Solo!!