The Subtitle or menu subpicture is too complex !

I am running Encore version 2.0 and almost completed a project. The final stage
is to add subtitles. When I try to create an iso file or burn to DVD, the
encoding process goes OK until it comes to encoding subtitles. It then comes up
with "The subtitles or menui sub-picture is too complex to be encoded"
and gives up.

I have tried replacing the subtitle text for the clip that seems to have the
problem. When the text is removed, all is OK. When I re-type the text for the
clip, the problem returns.

Anyone any idea what the problem could be?

I am running Windows XP with a 3GHz processor and 2GB RAM

Thanks in advance