Anita, thank you very much for your advice - it is nice to know it may not be just me. But
1. I tried logging into Photobucket direct but get the same IE error box on upload. It is rather general about some of the things that make IE unable to display the webpage.
No URL box ever appears, only an HTML one.
I agree I could get an existing picture from my Photobucket library into a Forum post - a URL box does still appear then.
2. I notice several comments on the Photobucket Login page which say they do not like the new system.
3. I am sure the advertising on Photobucket is more aggressive and quite undesirable. It is worrying that with these jittery laptop touchpads one might inadvertently select something unwanted.