Roman numerals suddenly appeared...

Your IMDb registration doesn't really have much to do with your IMDb name page. Roman numerals are added to the name pages when more than one person with the same name are entered into the database.

What's odd in this case, though, is that there doesn't seem to be any Rob Neilson (I) in the database, only (II) and (III). What might have happened is that someone added a credit to Rob Neilson (you), but didn't know if it was you or another person, and decided to add it as another person, which then became (III). Then someone may have noticed that this was in fact your credit and tried to combine the two profiles into one. If that's the case, the merge succeeded, but for some reason the merged profile kept the (III) numeral rather than the (I).

I'm not sure if this can be fixed by anyone outside the staff, through the normal edit functions. Hopefully someone from staff will see this post and can shine some light on the matter.