I am also on Wanadoo/Orange and generally have no problems at all. I say generally because there appear to be odd days and times in the week (not all weeks and varying days) when I have trouble connecting as well. I recently changed from the `old` 1MB service (expensive at £17.99pm) to the 2MB service at (£14.99pm) when I found I could. This was seamless but it was after this that I noted the inability to connect on occasion.
I put it down to one, or both, of loading and servicing. It could be that Orange is heavily loaded at specific times by businesses downloading data and/or they take servers offline to work on them. I don`t know if the newish high speed lines (8MB) also have an effect especially as more people appear to be going for the higher speeds.
The only other problem, again infrequent, is BT getting loaded up and I have to dial a couple of times to connect.
Hope this helps.