I created a encore project a few months ago and when played in WMP you couldn't scrub the timeline or fast forward/rewind. I check the user settings and activated 'All' which seemed to cure the problem. However I've just created another disc in the series using the same settings and once again I can't scrub the timeline. Moreover playing the first project disc again now that too won't scrub.
If you pick up the play head button and move it down or back along the timeline it just flicks back to the current time.
Interestingly I've just put the disc in an old machine which gave me the option of playing in Windows Media Classic, guess what, it scrubs fine.
Another classic case of MS updating stuff and screwing it up.
To answer my own question the problem lies with the user preferences. I've not exhausted all the permutations but if all user operations are switched on the scrubbing problem doesn't arise. I usually have chapter and timeline searching switched off to force users to use the menu hierarchy. However it seems that 'no scrubbing' is the unintended consequence of this.