The binding context. Anything late bound (eg any property that returns a generic Object type) will not provide intellisense since the compiler doesn't know at design time what type of object it actually is.

but Excel does know what the Activesheet is, but has never prompted me for a parameter

Ive always had to use Application.Worksheets(1).

I think there are other reasons Im not being prompted

Do any particular references have to be included?

but Excel does know what the Activesheet is

Actually, no it doesn't know. When you are writing the code, the compiler doesn't know what kind of sheet will be active when the code runs. It could be a worksheet, or a chart, or a macro sheet, or a dialog sheet. That is why the ActiveSheet property returns an Object (You can check that in the Object Browser)

Currently I get prompts for:

Application.

and that's it, nothing after that, no matter what parameter I choose

I used to (Office 97-2003)  get loads of prompts for parameters so my work environment is restricted but I cant figure why?

Any ideas why that might be?

So nothing if you type Application.WorksheetFunction then a dot?

Yes I do get that! Thanks